[llvm] [DirectX] Add `WaveActiveOp` builtin (PR #112058)

[Justin Bogner via llvm-commits]

bogner wrote:

I don't think this is the right approach. Replicating DXIL's WaveActiveOp as a DirectX intrinsic means we need to expose the enum of valid operations outside of the DXIL backend so that the front and middle end can generate them, and leaves us with IR that's kind of a pain to read since you need to interpret some arbitrary integer to understand it. I suspect we want separate intrinsics for each operation, or some other abstraction to represent these at a higher level

https://github.com/llvm/llvm-project/pull/112058