Generalize a few debug info test cases

Checking for the annotation comment rather than the metadata values makes these
tests resilient to a coming refactor that will pull these fields out into a
separate metadata node.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177237 91177308-0d34-0410-b5e6-96231b3b80d8