[clang] [Clang][AMDGPU] Add builtins for instrinsic `llvm.amdgcn.raw.buffer.store` (PR #94576)

[Krzysztof Drewniak via cfe-commits]

krzysz00 wrote:

(My guesses for how I might use sofffset is if I've got multiple identical buffers concatentated and I need to pick between them without messing with the extent field)

https://github.com/llvm/llvm-project/pull/94576