[InstCombine] enhance bitwise select matching

I noticed that adding a seemingly unrelated fold for xor caused
regressions on similar patterns, and this is one of the
underlying causes.

This could also be a variation for code as seen in:
https://llvm.org/PR34047
...although that exact example should be fixed after:
D113035 / c36b7e21

The vector test shows that we are actually missing a potential
canonicalization for bitcast-of-sext-of-not or the inverse.
The scalar test shows that even if we had that canonicalization,
it would still be possible to see this pattern due to extra uses.

https://alive2.llvm.org/ce/z/y2BAgi