[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