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.

llvm-svn: 213951