InstCombine: Combine (X | Y) - X to (~X & Y)

This implements the transformation from (X | Y) - X to (~X & Y).

Differential Revision: http://reviews.llvm.org/D5791

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221129 91177308-0d34-0410-b5e6-96231b3b80d8