Reapply r189013 (reverted in r189906) now that the underlying issue is fixed and tested (in r189996)

Debug info emission was tripping over an IRGen bug (fixed in r189996)
that was resulting in duplicate emission of static data members of class
templates in namespaces.

We could add more test coverage to debug info for this issue
specifically, but I think the underlying IRGen test is more targeted and
sufficient for the issue.