[clang] [CIR] Upstream emitAndUpdateRetAlloca (PR #129933)

[Amr Hesham via cfe-commits]

AmrDeveloper wrote:

> I have mixed feelings about this change. It mostly overlaps with what I am working on, which is class `LexicalScope`, which has a bunch of the code for handling the return value. I think I would prefer that this PR be dropped, as the changes will be part of the PR I am working on.

Yes, I think in this case it's better to drop this PR

Thank you

https://github.com/llvm/llvm-project/pull/129933