[X86] Fix InsertBitToMaskVector to only issue KSHIFTS of native size so that...

[X86] Fix InsertBitToMaskVector to only issue KSHIFTS of native size so that upper bits are properly zeroed.

There's no v2i1 or v4i1 kshift, and v8i1 is only supported with AVXDQ. Isel has fake patterns to extend these types to native shifts, but makes no guarantees about the value of any bits shifted in when shifting right.

This patch promotes the vector to a type that supports a native shift first and only allows inserting into the msb of a native sized shift.

I've constructed this in a way that doesn't do the promotion if we're going to fallback to using a xmm/ymm/zmm shuffle. I think I have a plan to remove the shuffle fall back entirely. In which case we this can be simplified, but I wanted to fix the correctness issue first.

llvm-svn: 320081