[lld-macho][nfc] Create Relocations.{h,cpp} for relocation-specific code

This more closely mirrors the structure of lld-ELF.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.

[lld-macho][nfc] Create Relocations.{h,cpp} for relocation-specific code

This more closely mirrors the structure of lld-ELF.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D98384

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[lld-macho] Fix semantics & add tests for ARM64 GOT/TLV relocs

I've adjusted the RelocAttrBits to better fit the semantics of
the relocations. In particular:

1. *_UNSIGNED relocations are no longer

[lld-macho] Fix semantics & add tests for ARM64 GOT/TLV relocs

I've adjusted the RelocAttrBits to better fit the semantics of
the relocations. In particular:

1. *_UNSIGNED relocations are no longer marked with the `TLV` bit, even
though they can occur within TLV sections. Instead the `TLV` bit is
reserved for relocations that can reference thread-local symbols, and
*_UNSIGNED relocations have their own `UNSIGNED` bit. The previous
implementation caused TLV and regular UNSIGNED semantics to be
conflated, resulting in rebase opcodes being incorrectly emitted for TLV
relocations.

2. I've added a new `POINTER` bit to denote non-relaxable GOT
relocations. This distinction isn't important on x86 -- the GOT
relocations there are either relaxable or non-relaxable loads -- but
arm64 has `GOT_LOAD_PAGE21` which loads the page that the referent
symbol is in (regardless of whether the symbol ends up in the GOT). This
relocation must reference a GOT symbol (so must have the `GOT` bit set)
but isn't itself relaxable (so must not have the `LOAD` bit). The
`POINTER` bit is used for relocations that *must* reference a GOT
slot.

3. A similar situation occurs for TLV relocations.

4. ld64 supports both a pcrel and an absolute version of
ARM64_RELOC_POINTER_TO_GOT. But the semantics of the absolute version
are pretty weird -- it results in the value of the GOT slot being
written, rather than the address. (That means a reference to a
dynamically-bound slot will result in zeroes being written.) The
programs I've tried linking don't use this form of the relocation, so
I've dropped our partial support for it by removing the relevant
RelocAttrBits.

Reviewed By: alexshap

Differential Revision: https://reviews.llvm.org/D97031

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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] Try to fix Windows build

[lld-macho][NFC] refactor relocation handling

Add per-reloc-type attribute bits and migrate code from per-target file into target independent code, driven by reloc attributes.

Many cleanups

Differ

[lld-macho][NFC] refactor relocation handling

Add per-reloc-type attribute bits and migrate code from per-target file into target independent code, driven by reloc attributes.

Many cleanups

Differential Revision: https://reviews.llvm.org/D95121

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Reland D75382 "[lld] Initial commit for new Mach-O backend"

With a fix for http://lab.llvm.org:8011/builders/clang-cmake-armv8-lld/builds/3636

Also trims some unneeded dependencies.

[lld] Initial commit for new Mach-O backend

Summary:
This is the first commit for the new Mach-O backend, designed to roughly
follow the architecture of the existing ELF and COFF backends, and
build

[lld] Initial commit for new Mach-O backend

Summary:
This is the first commit for the new Mach-O backend, designed to roughly
follow the architecture of the existing ELF and COFF backends, and
building off work that @ruiu and @pcc did in a branch a while back. Note
that this is a very stripped-down commit with the bare minimum of
functionality for ease of review. We'll be following up with more diffs
soon.

Currently, we're able to generate a simple "Hello World!" executable
that runs on OS X Catalina (and possibly on earlier OS X versions; I
haven't tested them). (This executable can be obtained by compiling
`test/MachO/relocations.s`.) We're mocking out a few load commands to
achieve this -- for example, we can't load dynamic libraries, but
Catalina requires binaries to be linked against `dyld`, so we hardcode
the emission of a `LC_LOAD_DYLIB` command. Other mocked out load
commands include LC_SYMTAB and LC_DYSYMTAB.

Differential Revision: https://reviews.llvm.org/D75382

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