[llvm] [profcheck] Add unknown branch weights to expanded cmpxchg loop. (PR #165841)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

This should probably remove the test case(s) it fixed from the `profcheck-xfail.txt` list?

https://github.com/llvm/llvm-project/pull/165841