[x86] Add an SSSE3 run and check mode to the 128-bit v2 tests of the new
vector shuffle lowering. This will be needed for up-coming palignr
tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218037 91177308-0d34-0410-b5e6-96231b3b80d8