[llvm] Reland "[SimplifyCFG] Check if the return instruction causes undefined behavior" (PR #76656)

[Quentin Dian via llvm-commits]

DianQK wrote:

Hmm, it looks like we're going to create `release/18`, so let me merge it first. If we find new issues, we can revert it.

https://github.com/llvm/llvm-project/pull/76656