[InstCombine] simplify code for A & (A ^ B) --> A & ~B

This fold was written in an odd way and tried to avoid
an endless loop by bailing out on all constants instead
of the supposedly problematic case of -1. But (X & -1) 
should always be simplified before we reach here, so I'm
not sure how that is a problem.

There were no tests for the commuted patterns, so I added
those at rL338364.

llvm-svn: 338367