[llvm] [FuncSpec] Skip SCCP on blocks of dead functions and poison their callsites (PR #154668)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> It seems that (post) dom tree analysis is not updated. I am still trying to compile LLVM with EXPENSIVE_CHECKS to reproduce. Hopefully, I will post the fix today. @mikaelholmen, feel free to revert if it's emergent.

I suspect we might now need to also set MadeChanges when DeadFunctions is not empty.

https://github.com/llvm/llvm-project/pull/154668