[DAG] allow more select folding for targets that have 'and not' (PR31175)

The original motivation for this patch comes from wanting to canonicalize 
more IR to selects and also canonicalizing min/max.

If we're going to do that, we need more backend fixups to undo select codegen 
when simpler ops will do. I chose AArch64 for the tests because that shows the
difference in the simplest way. This should fix:
https://llvm.org/bugs/show_bug.cgi?id=31175

Differential Revision: https://reviews.llvm.org/D27489

llvm-svn: 289738