PR19562: Fix another temporary node leak in Clang debug info emission

While constructing ObjC Interface types we might create the declaration
of some normal C++ types, thus adding things to the ReplaceMap. Make
sure we process the ReplaceMap after the ObjC interfaces.

In theory we know at this point, since we're at the end of the TU, that
we won't be upgrading any declarations to definitions, so we could just
construct non-temporary nodes, but that would require extra state in
CGDebugInfo to conditionalize the creation of declaration nodes which
seems annoying/more work than is appropriate.