[clang] [Clang][HIP] Deprecate the AMDGCN_WAVEFRONT_SIZE macros (PR #112849)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

> I made #113156 to hopefully address the OpenMP issue. We use it in the runtime itself for a lot of stuff so removing it would definitely break that. The function call here matches what NVIDIA provides via PTX. I think we should have an optimization that replaces the intrinsic with a constant if the function it belongs to has `wavefrontsize32` or whatever attributes.

We already do this during legalisation / legacy ISEL; there might be merit into doing it as early as possible though.

https://github.com/llvm/llvm-project/pull/112849