[NFC][InstCombine] Tests for x u<= x & C to x u<= C fold.

https://bugs.llvm.org/show_bug.cgi?id=38123
https://rise4fun.com/Alive/Fqp

This pattern is not commutative. But InstSimplify will
already have taken care of the 'commutative' variant.

llvm-svn: 337101