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

[Antonio Frighetto via cfe-commits]

antoniofrighetto wrote:

I think manually checking if `TrivialAutoVarInit` is set (to `Pattern`?) may be a better fix, as there was only [one codepath](https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CGDecl.cpp#L1972-L1974) in which we were not checking this.

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