[NFC][InstCombine] Tests for x & (-1 >> y) == x -> x u<= (-1 >> y) fold

https://bugs.llvm.org/show_bug.cgi?id=38123

This pattern will be produced by Implicit Integer Truncation sanitizer,
https://reviews.llvm.org/D48958
https://bugs.llvm.org/show_bug.cgi?id=21530
in unsigned case, therefore it is probably a good idea to improve it.

https://rise4fun.com/Alive/Rny

llvm-svn: 336796