[libc++] Towards a simpler extern template story in libc++

The flexibility around extern template instantiation declarations in
libc++ result in a very complicated model, especially when support for

[libc++] Towards a simpler extern template story in libc++

The flexibility around extern template instantiation declarations in
libc++ result in a very complicated model, especially when support for
slightly different configurations (like the debug mode or assertions
in the dylib) are taken into account. That results in unexpected bugs
like http://llvm.org/PR50534 (and there have been multiple similar
bugs in the past, notably around the debug mode).

This patch gets rid of the _LIBCPP_DISABLE_EXTERN_TEMPLATE knob, which
I don't think is fundamental. Indeed, the motivation for that knob was to
avoid taking a dependency on the library, however that can be done better
by linking against the static library instead. And in fact, some parts of
the headers will always depend on things defined in the library, which
defeats the original goal of _LIBCPP_DISABLE_EXTERN_TEMPLATE.

Differential Revision: https://reviews.llvm.org/D103960

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[libc++] Ensure that all public C++ headers include <__assert>

This patch changes the requirement for getting the declaration of the
assertion handler from including <__assert> to including any publ

[libc++] Ensure that all public C++ headers include <__assert>

This patch changes the requirement for getting the declaration of the
assertion handler from including <__assert> to including any public
C++ header of the library. Note that C compatibility headers are
excluded because we don't implement all the C headers ourselves --
some of them are taken straight from the C library, like assert.h.

It also adds a generated test to check it. Furthermore, this new
generated test is designed in a way that will make it possible to
replace almost all the existing test-generation scripts with this
system in upcoming patches.

Differential Revision: https://reviews.llvm.org/D122506

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[libc++] Normalize all our '#pragma GCC system_header', and regression-test.

Now we'll notice if a header forgets to include this magic phrase.

Differential Revision: https://reviews.llvm.org/D1188

[libc++] Normalize all our '#pragma GCC system_header', and regression-test.

Now we'll notice if a header forgets to include this magic phrase.

Differential Revision: https://reviews.llvm.org/D118800

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[libc++] Modularize <chrono>

I didn't split the calendar bits more than this because there was little
benefit to doing it, and I know our calendar support is incomplete.
Whoever picks up the missing

[libc++] Modularize <chrono>

I didn't split the calendar bits more than this because there was little
benefit to doing it, and I know our calendar support is incomplete.
Whoever picks up the missing calendar bits can organize these headers
at their leisure.

Differential Revision: https://reviews.llvm.org/D116965

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[libc++] Add the version header to all headers.

Some headers which require the version header depend on other headers to
provide it. Include the version header in all top-level headers to make
sure

[libc++] Add the version header to all headers.

Some headers which require the version header depend on other headers to
provide it. Include the version header in all top-level headers to make
sure a header cleanup can't remove the version header.

Note this doesn't add the version header to the c headers.

Reviewed By: #libc, Quuxplusone, ldionne

Differential Revision: https://reviews.llvm.org/D116172

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[runtimes][NFC] Remove filenames at the top of the license notice

We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste st

[runtimes][NFC] Remove filenames at the top of the license notice

We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste stuff.
This cleans up all the existing files so as to stop the spreading
as people copy-paste headers around.

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[libc++] Alphabetize and include-what-you-use. NFCI.

Differential Revision: https://reviews.llvm.org/D102781

[libc++] NFC: Normalize `#endif //` comment indentation

[libc++] Fix the header guard from _LIBCPP_STEAMBUF to _LIBCPP_STREAMBUF.

[libc++] Replace several uses of 0 by nullptr

Differential Revision: https://reviews.llvm.org/D43159

[libc++] Drop old workaround for iostreams instantiations missing from the dylib

On old Apple platforms (pre 10.9), we couldn't rely on the iostreams
explicit instantiations being part of the dylib.

[libc++] Drop old workaround for iostreams instantiations missing from the dylib

On old Apple platforms (pre 10.9), we couldn't rely on the iostreams
explicit instantiations being part of the dylib. However, we don't
support back-deploying to such old deployment targets anymore, so the
workaround can be dropped.

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Update more file headers across all of the LLVM projects in the monorepo
to reflect the new license. These used slightly different spellings that
defeated my regular expressions.

We understand that

Update more file headers across all of the LLVM projects in the monorepo
to reflect the new license. These used slightly different spellings that
defeated my regular expressions.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351648

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[libcxx] Don't depend on availability markup to provide the streams in the dylib

Whether an explicit instantiation declaration should be provided is not
a matter of availability markup.

This proble

[libcxx] Don't depend on availability markup to provide the streams in the dylib

Whether an explicit instantiation declaration should be provided is not
a matter of availability markup.

This problem is exemplified by the fact that some tests were incorrectly
marked as XFAIL when they should instead have been using the definition
of streams from the headers, and hence passing, and that, regardless of
whether visibility annotations are enabled.

llvm-svn: 348436

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[libcxx] Remove _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY

That macro has been defined to _LIBCPP_HIDE_FROM_ABI_AFTER_V1 for many
weeks now, so we're actually replacing uses of it for uses of
_LIBCPP

[libcxx] Remove _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY

That macro has been defined to _LIBCPP_HIDE_FROM_ABI_AFTER_V1 for many
weeks now, so we're actually replacing uses of it for uses of
_LIBCPP_HIDE_FROM_ABI_AFTER_V1 directly.

This should not change or break anything since the two macros are
100% equivalent, unless somebody is (incorrectly!) relying on
_LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY being defined.

llvm-svn: 344641

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[libc++] Take 2: Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY

Summary:
We never actually mean to always inline a function -- all the uses of
the macro I could find are actually

[libc++] Take 2: Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY

Summary:
We never actually mean to always inline a function -- all the uses of
the macro I could find are actually attempts to control the visibility
of symbols. This is better described by _LIBCPP_INLINE_VISIBILITY, which
is actually always defined the same.

This change is orthogonal to the decision of what we're actually going
to do with _LIBCPP_INLINE_VISIBILITY -- it just simplifies things by
having one canonical way of doing things.

Note that this commit had originally been applied in r336369 and then
reverted in r336382 because of unforeseen problems. Both of these problems
have now been fixed.

Reviewers: EricWF, mclow.lists

Subscribers: christof, dexonsmith, erikvanderpoel

Differential Revision: https://reviews.llvm.org/D48892

llvm-svn: 336866

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Revert "[libc++] Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY"

This reverts commit r336369. The commit had two problems:
1. __pbump was marked as _LIBCPP_EXTERN_TEMPLATE_INLINE

Revert "[libc++] Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY"

This reverts commit r336369. The commit had two problems:
1. __pbump was marked as _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY instead of
_LIBCPP_INLINE_VISIBILITY, which lead to two symbols being added in the
dylib and the check-cxx-abilist failing.

2. The LLDB tests started failing because they undefine
`_LIBCPP_INLINE_VISIBILITY`. I need to figure out why they do that and
fix the tests before we can go forward with this change.

llvm-svn: 336382

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[libc++] Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY

Summary:
We never actually mean to always inline a function -- all the uses of
the macro I could find are actually attempt

[libc++] Replace uses of _LIBCPP_ALWAYS_INLINE by _LIBCPP_INLINE_VISIBILITY

Summary:
We never actually mean to always inline a function -- all the uses of
the macro I could find are actually attempts to control the visibility
of symbols. This is better described by _LIBCPP_INLINE_VISIBILITY, which
is actually always defined the same.

This change is orthogonal to the decision of what we're actually going
to do with _LIBCPP_INLINE_VISIBILITY -- it just simplifies things by
having one canonical way of doing things.

Reviewers: EricWF

Subscribers: christof, llvm-commits, dexonsmith, erikvanderpoel, mclow.lists

Differential Revision: https://reviews.llvm.org/D48892

llvm-svn: 336369

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Add static_asserts to basic_ios and basic_stream_buf to ensure that that the traits match the character type. This is a requirement on the user - now we get consistent failures at compile time instea

Add static_asserts to basic_ios and basic_stream_buf to ensure that that the traits match the character type. This is a requirement on the user - now we get consistent failures at compile time instead of incomprehensible error messages or runtime failures. This is also LWG#2994 - not yet adopted.

llvm-svn: 323945

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Make pbump (internally) handle sizes bigger than MAX_INT. Fixes PR#33725 - thanks to Jonathan Wakely for the report

llvm-svn: 313031

make sure that we don't call basic_streambuf::gbump with a value bigger than INT_MAX, since it only takes an int. Related to, but not quite the same as PR33725

llvm-svn: 308880

[Libc++] Use #pragma push_macro/pop_macro to better handle min/max on Windows

Summary:
This patch improves how libc++ handles min/max macros within the headers. Previously libc++ would undef them an

[Libc++] Use #pragma push_macro/pop_macro to better handle min/max on Windows

Summary:
This patch improves how libc++ handles min/max macros within the headers. Previously libc++ would undef them and emit a warning.
This patch changes libc++ to use `#pragma push_macro` to save the macro before undefining it, and `#pragma pop_macro` to restore the macros and the end of the header.

Reviewers: mclow.lists, bcraig, compnerd, EricWF

Reviewed By: EricWF

Subscribers: cfe-commits, krytarowski

Differential Revision: https://reviews.llvm.org/D33080

llvm-svn: 304357

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Add markup for libc++ dylib availability

Libc++ is used as a system library on macOS and iOS (amongst others). In order
for users to be able to compile a binary that is intended to be deployed to an

Add markup for libc++ dylib availability

Libc++ is used as a system library on macOS and iOS (amongst others). In order
for users to be able to compile a binary that is intended to be deployed to an
older version of the platform, clang provides the
availability attribute <https://clang.llvm.org/docs/AttributeReference.html#availability>_
that can be placed on declarations to describe the lifecycle of a symbol in the
library.

See docs/DesignDocs/AvailabilityMarkup.rst for more information.

Differential Revision: https://reviews.llvm.org/D31739

llvm-svn: 302172

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[NFC] Rename _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS

The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__typ

[NFC] Rename _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS

The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__type_visibility__)) with Clang. The only remaining difference
is that _LIBCPP_TYPE_VIS_ONLY can be applied to templates whereas
_LIBCPP_TYPE_VIS cannot (due to dllimport/dllexport not being allowed on
templates).

This patch renames _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS.

llvm-svn: 291035

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[libc++] Add _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY to support GCC ABI compatibility

Summary:
GCC and Clang handle visibility attributes on the out-of-line definition of externally instantiated t

[libc++] Add _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY to support GCC ABI compatibility

Summary:
GCC and Clang handle visibility attributes on the out-of-line definition of externally instantiated templates differently. For example in the reproducer below Clang will emit both 'foo' and 'bar' with default visibility while GCC only emits a non-hidden 'foo'.

```
// RUN: g++ -std=c++11 -shared -O3 test.cpp && sym_extract.py a.out
// RUN: clang++ -std=c++11 -shared -O3 test.cpp && sym_extract.py a.out
#define INLINE_VISIBILITY __attribute__((visibility("hidden"), always_inline))

template <class T>
struct Foo {
void foo();
void bar();
};

template <class T>
void Foo<T>::foo() {}

template <class T>
inline INLINE_VISIBILITY
void Foo<T>::bar() {}

template struct Foo<int>;
```

This difference creates ABI incompatibilities between Clang and GCC built dylibs. Specifically GCC built dylibs lack definitions for various member functions of `basic_string`, `basic_istream`, `basic_ostream`, `basic_iostream`, and `basic_streambuf` (All of these types are externally instantiated).

Surprisingly these missing symbols don't cause many problems because the functions are marked `always_inline` therefore the dylib definition is rarely needed. However when an out-of-line definition is required then GCC built dylibs will fail to link. For example [GCC built dylibs cannot build Clang](http://stackoverflow.com/questions/39454262/clang-build-errors).

This patch works around this issue by adding `_LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY` which is used to mark externally instantiated member functions as always inline. When building the library `_LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY` sets the symbol's visibility to "default" instead of "hidden", otherwise it acts exactly the same as `_LIBCPP_INLINE_VISIBILITY`.

After applying this patch GCC dylibs now contain:
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE7sungetcEv`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5gbumpEi`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE7sungetcEv`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE9sputbackcEc`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEE3getERNS_15basic_streambufIwS2_EE`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEElsEPFRNS_9basic_iosIwS2_EES6_E`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE4setpEPcS4_`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEEC1EPNS_15basic_streambufIwS2_EE`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE6snextcEv`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEE4swapERS3_`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEE4swapERS3_`
* `_ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcm`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEErsEPFRNS_8ios_baseES5_E`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE9pubsetbufEPcl`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE10pubseekoffExNS_8ios_base7seekdirEj`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEErsEPFRNS_9basic_iosIwS2_EES6_E`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5pbumpEi`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE5seekpENS_4fposI11__mbstate_tEE`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEE7getlineEPcl`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5sgetcEv`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEE3getERNS_15basic_streambufIcS2_EE`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEElsEPFRNS_8ios_baseES5_E`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE8in_availEv`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEErsEPFRNS_8ios_baseES5_E`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE6sbumpcEv`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEElsEPFRNS_9basic_iosIcS2_EES6_E`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEE3getERc`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE6snextcEv`
* `_ZNSt3__112basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEE6__initEmw`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEE7getlineEPwl`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE5tellpEv`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEE3getERw`
* `_ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEmc`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE7pubsyncEv`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEE3getEPcl`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEEC2EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEErsEPFRNS_9basic_iosIcS2_EES6_E`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE7pubsyncEv`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5sputcEc`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEE5seekpExNS_8ios_base7seekdirE`
* `_ZNKSt3__115basic_streambufIcNS_11char_traitsIcEEE6getlocEv`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5gbumpEi`
* `_ZNSt3__114basic_iostreamIcNS_11char_traitsIcEEE4swapERS3_`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEE5seekpENS_4fposI11__mbstate_tEE`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEE5tellpEv`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEElsEPFRS3_S4_E`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEE3getEPwl`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEEC2EPNS_15basic_streambufIwS2_EE`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEElsEPFRS3_S4_E`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE4setgEPcS4_S4_`
* `_ZNSt3__112basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEE6__initEPKwmm`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE4setgEPwS4_S4_`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEEC1EPNS_15basic_streambufIwS2_EE`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE8pubimbueERKNS_6localeE`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE4swapERS3_`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEEC2EPNS_15basic_streambufIwS2_EE`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE10pubseekposENS_4fposI11__mbstate_tEEj`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5pbumpEi`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5sgetcEv`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEE4swapERS3_`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE10pubseekposENS_4fposI11__mbstate_tEEj`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5sputnEPKcl`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEE5seekpExNS_8ios_base7seekdirE`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5sgetnEPwl`
* `_ZNSt3__113basic_ostreamIwNS_11char_traitsIwEEElsEPFRNS_8ios_baseES5_E`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE4setpEPwS4_`
* `_ZNSt3__115basic_streambufIcNS_11char_traitsIcEEE5sgetnEPcl`
* `_ZNKSt3__115basic_streambufIwNS_11char_traitsIwEEE6getlocEv`
* `_ZNSt3__114basic_iostreamIcNS_11char_traitsIcEEEC2EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE8pubimbueERKNS_6localeE`
* `_ZNSt3__114basic_iostreamIcNS_11char_traitsIcEEEC1EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE8in_availEv`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEEC1EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE6__initEPKcmm`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE6sbumpcEv`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE10pubseekoffExNS_8ios_base7seekdirEj`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEEC2EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__113basic_istreamIwNS_11char_traitsIwEEErsEPFRS3_S4_E`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE9sputbackcEw`
* `_ZNSt3__112basic_stringIwNS_11char_traitsIwEENS_9allocatorIwEEE6__initEPKwm`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5sputnEPKwl`
* `_ZNSt3__113basic_istreamIcNS_11char_traitsIcEEErsEPFRS3_S4_E`
* `_ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEEC1EPNS_15basic_streambufIcS2_EE`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE9pubsetbufEPwl`
* `_ZNSt3__115basic_streambufIwNS_11char_traitsIwEEE5sputcEw`


This patch has no effect on Clang based builds.



Reviewers: mclow.lists, eugenis, danalbert, jroelofs, EricWF

Subscribers: beanz, cfe-commits, mgorny

Differential Revision: https://reviews.llvm.org/D24600

llvm-svn: 281681

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[libc++] Fix and document visibility attributes for Clang, GCC and Windows.

Summary:
This patch fixes a number of problems with the visibility macros across GCC (on Unix) and Windows (DLL import/exp

[libc++] Fix and document visibility attributes for Clang, GCC and Windows.

Summary:
This patch fixes a number of problems with the visibility macros across GCC (on Unix) and Windows (DLL import/export semantics). All of the visibility macros are now documented under `DesignDocs/VisibilityMacros.rst`. Now I'll no longer forget the subtleties of each!

This patch adds two new visibility macros:

* `_LIBCPP_ENUM_VIS` for controlling the typeinfo of enum types. Only Clang supports this.
* `_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS` for redefining visibility on explicit instantiation declarations. Clang and Windows require this.

After applying this patch GCC only emits one -Wattribute warning opposed to 30+.


Reviewers: mclow.lists, EricWF

Subscribers: beanz, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D24602

llvm-svn: 281673

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