[clang] [llvm] [AMDGPU] Add `nocreateundeforpoison` annotations (PR #166450)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

(I think the main review item is everyone else convincing themselves that the intrinsics I said don't create poison in fact don't)

https://github.com/llvm/llvm-project/pull/166450