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

[Krzysztof Drewniak via cfe-commits]

krzysz00 wrote:

`voffset` and `soffset` are "offset that goes in VGPRs" and "offset that goes in SGPRs", with the latter having some different bounds-checking semantics on ... at least some of the gfx9's, IIRC.

The address space 7 lowering just uses voffset.

Re arbitrary aggregates: LLPC has code for handling this (since I'm pretty sure stuff like Vulkan wants it, and "aggregates" here might even be unusual cases like `<4 x i8>` instead of `i32`) so It's been on the roadmap for some time.

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