[llvm] [X86] Fix XOR folding in EmitCmp (PR #210546)

[via llvm-commits]

AZero13 wrote:

The logic works but I would not do the inline =. I would change the style to make this clearer. Plus I wonder if maybe we should return that value instead of doing DAG.replacewith and then return cmp.value(1)

https://github.com/llvm/llvm-project/pull/210546