DebugInfo: Fix up some test cases to have more correct debug info metadata.

* Add CUs to the named CU node
* Add missing DW_TAG_subprogram nodes
* Add llvm::Functions to the DW_TAG_subprogram nodes

This cleans up the tests so that they don't break under a
soon-to-be-made change that is more strict about such things.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213951 91177308-0d34-0410-b5e6-96231b3b80d8