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

[Krzysztof Drewniak via cfe-commits]

krzysz00 wrote:

(The ugly version of the arbitrary types code lives around https://github.com/GPUOpen-Drivers/llpc/blob/6c770c7d276d2c2504aed2a0278aab1610993ecf/lgc/patch/PatchBufferOp.cpp#L1559 and really should be an isel legalization instead)

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