[clang] [llvm] [AMDGPU] Introduce asyncmark/wait intrinsics (PR #173259)

[Krzysztof Drewniak via cfe-commits]

krzysz00 wrote:

@ssahasra Does the stuff I wrote above match your understanding of what we're going for, and will it help update the documentation?

https://github.com/llvm/llvm-project/pull/173259