Allow multiple check prefixes in FileCheck.

This is useful if you want to run multiple variations
of a single test, and the majority of check lines
should be the same.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194343 91177308-0d34-0410-b5e6-96231b3b80d8
Resolve TODO in test now that filecheck has multiple check prefixes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194344 91177308-0d34-0410-b5e6-96231b3b80d8