[lld-macho] Implement ICF

ICF = Identical C(ode|OMDAT) Folding

This is the LLD ELF/COFF algorithm, adapted for MachO. So far, only `-icf all` is supported. In order to support `-icf safe`, we will

[lld-macho] Implement ICF

ICF = Identical C(ode|OMDAT) Folding

This is the LLD ELF/COFF algorithm, adapted for MachO. So far, only `-icf all` is supported. In order to support `-icf safe`, we will need to port address-significance tables (`.addrsig` directives) to MachO, which will come in later diffs.

`check-{llvm,clang,lld}` have 0 regressions for `lld -icf all` vs. baseline ld64.

We only run ICF on `__TEXT,__text` for reasons explained in the block comment in `ConcatOutputSection.cpp`.

Here is the perf impact for linking `chromium_framekwork` on a Mac Pro (16-core Xeon W) for the non-ICF case vs. pre-ICF:
```
N Min Max Median Avg Stddev
x 20 4.27 4.44 4.34 4.349 0.043029977
+ 20 4.37 4.46 4.405 4.4115 0.025188761
Difference at 95.0% confidence
0.0625 +/- 0.0225658
1.43711% +/- 0.518873%
(Student's t, pooled s = 0.0352566)
```

Reviewed By: #lld-macho, int3

Differential Revision: https://reviews.llvm.org/D103292

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[lld-macho] Support loading of zippered dylibs

ld64 can emit dylibs that support more than one platform (typically macOS and
macCatalyst). This diff allows LLD to read in those dylibs. Note that thi

[lld-macho] Support loading of zippered dylibs

ld64 can emit dylibs that support more than one platform (typically macOS and
macCatalyst). This diff allows LLD to read in those dylibs. Note that this is a
super bare-bones implementation -- in particular, I haven't added support for
LLD to emit those multi-platform dylibs, nor have I added a variety of
validation checks that ld64 does. Until we have a use-case for emitting zippered
dylibs, I think this is good enough.

Fixes PR49597.

Reviewed By: #lld-macho, oontvoo

Differential Revision: https://reviews.llvm.org/D101954

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[lld-macho][nfc] Convert the mock libSystem.tbd to TBDv4

It doesn't seem like TBDv3 allows for specifying multiple platforms, so I'm
upgrading us to TBDv4. (We need to support multiple platforms in

[lld-macho][nfc] Convert the mock libSystem.tbd to TBDv4

It doesn't seem like TBDv3 allows for specifying multiple platforms, so I'm
upgrading us to TBDv4. (We need to support multiple platforms in order to test
that we can handle zippered dylibs; that functionality will be added in an
upcoming diff.)

Differential Revision: https://reviews.llvm.org/D101953

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[lld/mac] Use libSystem.dylib instead of libSystem.B.dylib in tests

For -flat_namespace, lld needs to load dylibs in LC_LOAD_DYLIB.
The current setup meant that libSystem.dylib would cause a LC_LOAD

[lld/mac] Use libSystem.dylib instead of libSystem.B.dylib in tests

For -flat_namespace, lld needs to load dylibs in LC_LOAD_DYLIB.
The current setup meant that libSystem.dylib would cause a LC_LOAD_DYLIB
with libSystem.B.dylib, but that didn't exist in our libsysroot for
tests. So just drop the .B.

See https://reviews.llvm.org/D97641#2595237 and
https://reviews.llvm.org/D97641#2595270

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[lld-macho] Add ARM64 target arch

This is an initial base commit for ARM64 target arch support. I don't represent that it complete or bug-free, but wish to put it out for review now that some basic

[lld-macho] Add ARM64 target arch

This is an initial base commit for ARM64 target arch support. I don't represent that it complete or bug-free, but wish to put it out for review now that some basic things like branch target & load/store address relocs are working.

I can add more tests to this base commit, or add them in follow-up commits.

It is not entirely clear whether I use the "ARM64" (Apple) or "AArch64" (non-Apple) naming convention. Guidance is appreciated.

Differential Revision: https://reviews.llvm.org/D88629

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[lld-macho] Support static linking of thread-locals

Note: What ELF refers to as "TLS", Mach-O seems to refer to as "TLV", i.e.
thread-local variables.

This diff implements support for TLV relocatio

[lld-macho] Support static linking of thread-locals

Note: What ELF refers to as "TLS", Mach-O seems to refer to as "TLV", i.e.
thread-local variables.

This diff implements support for TLV relocations that reference defined
symbols. On x86_64, TLV relocations are always used with movq opcodes, so for
defined TLVs, we don't need to create a synthetic section to store the
addresses of the symbols -- we can just convert the `movq` to a `leaq`.

One notable quirk of Mach-O's TLVs is that absolute-address relocations
inside TLV-defining sections behave differently -- their addresses are
no longer absolute, but relative to the start of the target section.
(AFAICT, RIP-relative relocations are not allowed in these sections.)

Reviewed By: #lld-macho, compnerd, smeenai

Differential Revision: https://reviews.llvm.org/D85080

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ld64.lld: Make janky support for tbd files actually work sometimes

Also fix a bug in the test input that made the test miss this issue.

lld: initial pass at supporting TBD

Add support to lld to use Text Based API stubs for linking. This is
support is incomplete not filtering out platforms. It also does not
account for architecture

lld: initial pass at supporting TBD

Add support to lld to use Text Based API stubs for linking. This is
support is incomplete not filtering out platforms. It also does not
account for architecture specific API handling and potentially does not
correctly handle trees of re-exports with inlined libraries being
treated as direct children of the top level library.

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