[clang] [clang][CodeGen] Allow memcpy replace with trivial auto var init (PR #84230)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

I think the changes here make sense (keeping in mind what @efriedma-quic says about long-term goals vs 18.x practicality). Eli, @serge-sans-paille, are you okay with the changes as well? (Please don't land on my approval without waiting a bit for Eli and Serge.)

If so, I'd like to get this backported into 18.x as well because of the issues we're seeing in the wild. Any disagreement?

https://github.com/llvm/llvm-project/pull/84230