[clang] [CIR] Add cir-simplify pass (PR #138317)

[Bruno Cardoso Lopes via cfe-commits]

https://github.com/bcardosolopes commented:

LGTM with minor tip: can you also add a source to CIR test that guarantee this kicks in from the driver? 

https://github.com/llvm/llvm-project/pull/138317