[x86] Clean up a test case to use check labels and spell out the exact
instruction sequences with CHECK-NEXT for these test cases.

This notably exposes how absolutely horrible the generated code is for
several of these test cases, and will make any future updates to the
test as our vector instruction selection gets better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213732 91177308-0d34-0410-b5e6-96231b3b80d8