[llvm] [Inline][Cloning] Drop incompatible attributes from `NewFunc` before `instSimplify` (PR #90489)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

FWIW, I couldn't find any better way to fix this without any radical change, as, indeed, the rewriting of returns happens too late. I think #87482 is an acceptable workaround, but I feel like it might just mask similar bugs surfacing. Though, while having noundef ret attribute w/ ret void is clearly illegal, arguably this could be permitted at this stage, as we're still in the process of disposing of the old returns / CFG fix-up.

https://github.com/llvm/llvm-project/pull/90489