[llvm] [LLVM][ConstantFold] Undefined values are not constant (PR #130713)

[Kees Cook via llvm-commits]

kees wrote:

(ah, my reviewers addition collided with the bot and @nikic got removed -- I've fix that now.)

Okay, it sounds like there isn't really an issue for this commit, just generally that `undef` is no good (which I agree with). So since it solves the specific corner case that Linux ran into and aligns Clang behavior with GCC, it seems like a net benefit. Okay to commit?

https://github.com/llvm/llvm-project/pull/130713