[llvm] [X86] Avoid useless DomTree in flags copy lowering (PR #97628)

[Alexis Engelke via llvm-commits]

aengelke wrote:

> `--debug-pass` does not work when `LLVM_ENABLE_ASSERTIONS` is off.

It just happened to work for me and it also works with Fedora's build of LLVM (I'm certain they build without assertions).

https://github.com/llvm/llvm-project/pull/97628