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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> 2. What I mean is that "types that work" isn't the right framing: any type can be legalized to one or more types that work. That is, down in the isel legalizer, if I call for, for example
>    ```llvm
>    %0 = call {i64, i64, i8} @llvm.amdgcn.raw.buffer.ptr.load(ptr addrspace(8) %rsrc, i32 %off, ...)
>    ```

Handling arbitrary aggregates here isn't really reasonable or necessary. We can restrict this to a reasonable set of legal-ish types 


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