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

[Morris Hafner via cfe-commits]

mmha wrote:

@bcardosolopes Adding a test for C++ -> CIR depends on #138003 which adds lowering for `?:`, `&&` and `||`. Since this one's ready to be merged apart from your remark IMO I'd add that test in #138003

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