[clang] [llvm] [opt][AMDGPU] Add pass to handle AMDGCN pseudo-intrinsics target specific info), start with `llvm.amdgcn.wavefrontsize` (PR #114481)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

> Just adding this to the pass pipeline where it is is no better than just doing it in instcombine, which is the natural place to do this. This patch, like instcombine, still has the problem that we don't know if we're producing the final code.

We could just turn this off for a particular compilation and maintain the current unfoldable state. Which makes it possibly preferable to keep this as a pass. Or do the two separate builds. We probably need to appreciate that the vast majority of clients are neither `libc` nor `ROCDL` in their needs, and might not be keen on multi-builds for something that is actually intended to be generic, like, in our case, AMDGCN flavoured SPIR-V.

https://github.com/llvm/llvm-project/pull/114481