[llvm] [Bitcode] Fix nondeterministic phi instruction order (PR #151006)

[Michael Hackner via llvm-commits]

HackAttack wrote:

Ok, I discovered something interesting/embarrassing: the nondeterminism seems to go away when running rustc against a custom-built LLVM _regardless of whether this patch is applied!_ So there’s currently not enough evidence to conclude that the bug is with LLVM. I’ll close this and link a bug against [rust-lang/rust](https://github.com/rust-lang/rust). Thank you for your time!

https://github.com/llvm/llvm-project/pull/151006