[InstCombine] canonicalize cmp-of-bitcast-of-vector-cmp to use zero constant

We can invert a compare constant and preserve the logic
as shown in this sampling:
https://alive2.llvm.org/ce/z/YAXbfs
(In theory, we could deal with non-all-ones/zero as well,
but it doesn't seem worthwhile.)

I noticed this as a part of the x86 codegen difference in
https://llvm.org/PR51259 - it ends up using "test"
instead of "not + cmp" in that example.

This pattern also shows up in https://llvm.org/PR41312
and https://llvm.org/PR50798 .

Differential Revision: https://reviews.llvm.org/D107170