[clang] [llvm] [clang][amdgpu] Add builtins for raw/struct buffer lds load (PR #137678)

[Krzysztof Drewniak via cfe-commits]

krzysz00 wrote:

Semantically, seems fine, but I can't review meaningfully on the clang side

https://github.com/llvm/llvm-project/pull/137678