[X86] Add a DAG combine to turn (and (bitcast (vXi1 (concat_vectors (vYi1 setcc)...

[X86] Add a DAG combine to turn (and (bitcast (vXi1 (concat_vectors (vYi1 setcc), undef,))), C) into (bitcast (vXi1 (concat_vectors (vYi1 setcc), zero,)))

The legalization of v2i1->i2 or v4i1->i4 bitcasts followed by a setcc can create an and after the bitcast. If we're lucky enough that the input to the bitcast is a concat_vectors where the first operand is a setcc that can natively 0 all the upper bits of ak-register, then we should replace the other operands of the concat_vectors with zero in order to remove the AND.

With the AND removed we might be able to use a kortest on the result.

Differential Revision: https://reviews.llvm.org/D69205