[x86] Add some important, missing test coverage for blending from one
vector to a zero vector for the v2 cases and fix the v4 integer cases to
actually blend from a vector.

There are already seprate tests for the case of inserting from a scalar.

These cases cover a lot of the regressions I've seen in the regression
test suite for the new vector shuffle lowering and specifically cover
the reported lack of using various zext-ing instruction patterns. My
next patch should fix a big chunk of this, but wanted to get a nice
baseline for these patterns in the test cases first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218976 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Significantly improve the ability of the new vector shuffle
lowering to match VZEXT_MOVL patterns.

I hadn't realized that these had sufficient pattern smarts in the
backend to lower zext-ing from the low element of a vector without it
being a scalar_to_vector node. They do, and this is how to match a bunch
of patterns for movq, movss, etc.

There is a weird propensity to end up using pshufd to place the element
afterward even though it means domain crossing (or rather, to use
xorps+movss to zext the element rather than movq) but that's an
orthogonal problem with VZEXT_MOVL that someone should probably look at.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218977 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Fix the RUN-lines of this test to make sense.

I got them quite wrong when updating it and had the SSE4.1 run checked
for SSE2 and the SSE2 run checked for SSE4.1. I think everything was
actually generic SSE, but this still seems good to fix. While here,
hoist the triple into the IR and make the flag set a bit more direct in
what it is trying to test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218978 91177308-0d34-0410-b5e6-96231b3b80d8