[DAGCombine] Fold (x & ~y) | y patterns

Fold (x & ~y) | y and it's four commuted variants to x | y. This pattern
can in particular appear when a vselect c, x, -1 is expanded to
(x & ~c) | (-1 & c) and combined to (x & ~c) | c.

This change has some overlap with D59066, which avoids creating a
vselect of this form in the first place during uaddsat expansion.

Differential Revision: https://reviews.llvm.org/D59174

llvm-svn: 356333