[llvm] [AMDGPU] Add function attribute to force enable WQM (PR #82468)

[Jay Foad via llvm-commits]

jayfoad wrote:

After some offline discussion, my understanding is that the existing `llvm.amdgcn.set.inactive` intrinsic is "soft" in that it does not force WQM for the shader. Perhaps we could fake up a "strict" version of it by applying `llvm.amdgcn.wqm` to its input and/or output?

https://github.com/llvm/llvm-project/pull/82468