Move relocation specifiers to AMDGPUMCExpr::Specifier
Similar to previous migration done for all other ELF targets.
Switch from the confusing `VariantKind` to `Specifier`, which aligns
with Arm and IBM AIX's documentation.
Moving forward, relocation specifiers should be integrated into
AMDGPUMCExpr rather than MCSymbolRefExpr::SubclassData.
(Note: the term AMDGPUMCExpr::VariantKind is for expressions
without relocation specifiers:
https://github.com/llvm/llvm-project/pull/82022
It's up to AMDGPU maintainers to integrate these constants into Specifier.
)
Pull Request: https://github.com/llvm/llvm-project/pull/133608
