[llvm] [amdgpu] Add llvm.amdgcn.init.whole.wave intrinsic (PR #105822)

[Jay Foad via llvm-commits]

jayfoad wrote:

Can this replacea llvm.amdgcn.init.exec? (Sorry if that's a dumb question, I have not grokked your new intrinsic yet.)

https://github.com/llvm/llvm-project/pull/105822