[x86] allow FP-logic ops when one operand is FP and result is FP

We save an inter-register file move this way. If there's any CPU where
the FP logic is slower, we could transform this back to int-logic in 
MachineCombiner.

This helps, but doesn't solve, PR6137:
https://llvm.org/bugs/show_bug.cgi?id=6137

The 'andn' test shows that we're missing a pattern match to
recognize the xor with -1 constant as a 'not' op.

llvm-svn: 287171