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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> If we do want addrspace(7), we'll need to expose `make.buffer.rsrc` and give it a `p7` variant probably.

Yes.

We probably should expose some kind of custom type instead of directly using a C address_space(7) attribute 

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