Improve test to actually check for a folded load.

Improve test to actually check for a folded load.

This test was checking for lack of a "movaps" (an aligned load)
rather than a "movups" (an unaligned load). It also included
a store which complicated the checking.

Add specific CPU runs to prevent subtarget feature flag overrides
from inhibiting this optimization.

llvm-svn: 227972