[InstCombine] foldICmpWithLowBitMaskedVal(): handle uncanonical ((1 << y)+(-1)) mask

Summary:
Same as to D52146.
`((1 << y)+(-1))` is simply non-canoniacal version of `~(-1 << y)`: https://rise4fun.com/Alive/0vl
We can not canonicalize it due to the extra uses. But we can handle it here.

Reviewers: spatel, craig.topper, RKSimon

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D52147

llvm-svn: 342547