Here we were winding up in get_tinfo_decl with a template type that was 
still incomplete because nothing else had required it to be complete. 
So we initially decide to treat it as a class with no bases.  But then 
the process of creating the initializer for the type_info node causes 
the type to be complete, so we generate an initializer for a class with 
bases, which doesn't match the type we already gave it.

Fixed by instantiating the type in get_tinfo_decl.

Tested x86_64-pc-linux-gnu, applying to trunk.