Simplify/generalize some debug info test cases

Mostly, try to depend on the annotation comments more so these tests are more
legible, brief, and agnostic to schema changes in the future (sure, they're not
agnostic to changes to the comment annotations but since they're easier to read
they should be easier to update if that happens).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177457 91177308-0d34-0410-b5e6-96231b3b80d8