[InstCombine] add/move folds for [not]-xor

[InstCombine] add/move folds for [not]-xor

We handled all of the commuted variants for plain xor already,
although they were scattered around and sometimes folded less
efficiently using distributive laws. We had no folds for not-xor.

Handling all of these patterns consistently is part of trying to
reinstate:
https://reviews.llvm.org/rL300977

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301144 91177308-0d34-0410-b5e6-96231b3b80d8