[llvm] Reland "[amdgpu] Add llvm.amdgcn.init.whole.wave intrinsic" (PR #108512)

[Jay Foad via llvm-commits]

jayfoad wrote:

> The problem was a conflict with [e55d6f5](https://github.com/llvm/llvm-project/commit/e55d6f5ea2656bf842973d8bee86c3ace31bc865) "[AMDGPU] Simplify and improve codegen for llvm.amdgcn.set.inactive (#107889)" which changed the syntax of V_SET_INACTIVE (and thus made my MIR test crash).

Sorry!

https://github.com/llvm/llvm-project/pull/108512