[llvm] [SelectionDAG] Make `(a & x) | (~a & y) -> (a & (x ^ y)) ^ y` available for all targets (PR #137641)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Maybe worth waiting until #143363 has dropped and then just add another SDPatternMatch pattern to fold MaskedMerge

https://github.com/llvm/llvm-project/pull/137641