[x86] prevent infinite looping from vselect commutation (PR41066)

This is an immediate fix for:
https://bugs.llvm.org/show_bug.cgi?id=41066
...but as noted there and the code comments, we should do better
by stubbing this out sooner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356158 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed