Really fix CHECK-LABEL and CHECK-DAG interaction. This actually just restores the initial implementation that was in r186162 but got lost in some subsequent refactoring. More explicit variable names and comments are present now to hopefully prevent repeat regression, as well as another test.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192477 91177308-0d34-0410-b5e6-96231b3b80d8