Currently pternlog intrinsics stay as a function call and are unable
to merge with other bin-ops / constant-fold.
This commit adds support for reducing all pternlog intrinsics to
their base logic-ops so that they can be further reduced in other
passes.
Since the x86 backend doesn't do a great job creating vpternlog
instructions from stray logic ops, the current logic only simplifies
in the cases were we obviously will be able to do as good or
better. As the x86 backend improves, more cases can be simplified.
Do we need to make sure we are looking at vectors of ConstantInts rather than vectors of ConstantExpr?