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

[Jin Huang via llvm-commits]

jinhuang1102 wrote:

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

Thanks for letting me know! Yes, I will remove all of these expected failed tests after the PR is merged! 

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