[X86,MC] Add relocation R_X86_64_REX2_GOTPCRELX (#106681)

For

	mov        name@GOTPCREL(%rip), %reg
	test       %reg, name@GOTPCREL(%rip)
	binop      name@GOTPCREL(%rip), %reg

where binop is one of adc, add, and, cmp, or, sbb, sub, xor
instructions, add

 `R_X86_64_REX2_GOTPCRELX`/`R_X86_64_CODE_4_GOTPCRELX` = 43

if the instruction starts at 4 bytes before the relocation offset. It
similar to R_X86_64_GOTPCRELX.

Linker can treat `R_X86_64_REX2_GOTPCRELX`/`R_X86_64_CODE_4_GOTPCRELX`
as `R_X86_64_GOTPCREL` or convert the above instructions to

	lea	name(%rip), %reg
	mov	$name, %reg
	test	$name, %reg
	binop	$name, %reg

if the first byte of the instruction at the relocation `offset - 4` is
`0xd5` (namely, encoded w/ REX2 prefix) when possible.

Binutils patch:
https://github.com/bminor/binutils-gdb/commit/3d5a60de52556f6a53d71d7e607c6696450ae3e4
Binutils mailthread:
https://sourceware.org/pipermail/binutils/2023-December/131462.html
ABI discussion: https://groups.google.com/g/x86-64-abi/c/KbzaNHRB6QU
Blog: https://kanrobert.github.io/rfc/All-about-APX-relocation
12 files changed
tree: 06d230bb5123cee91d3515eddf96d3d413260547
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. offload/
  21. openmp/
  22. polly/
  23. pstl/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-tidy
  29. .git-blame-ignore-revs
  30. .gitattributes
  31. .gitignore
  32. .mailmap
  33. CODE_OF_CONDUCT.md
  34. CONTRIBUTING.md
  35. LICENSE.TXT
  36. pyproject.toml
  37. README.md
  38. SECURITY.md
README.md

The LLVM Compiler Infrastructure

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Welcome to the LLVM project!

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