[llvm] [AMDGPU] Cgscc amdgpu attributor (PR #179719)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I think I'd like to get the boilerplate for running in CGSCC in, but not yet add it to the default pipeline 

https://github.com/llvm/llvm-project/pull/179719