[clang] [CIR] Handle return with cleanups (PR #163849)

[Bruno Cardoso Lopes via cfe-commits]

bcardosolopes wrote:

> That would simplify the EHScopeStck handling significantly in CIR, but the complexity would just be moved to the FlattenCFG pass, and this would mean we were diverging from the classic codegen code structure.

I'm up for the tradeoff here, the lower level alternative will make code way harder to analyze.

https://github.com/llvm/llvm-project/pull/163849