debug/8095: missing dwarf info for parent class

[Horsley Tom]

> > If there are ways to tie debug output to a certain member of a class
(just
> > as we do for vtables), then I would say this is a good idea. If someone
> > doesn't like this, then compile your library with -g.
> > 
> > But that's just my opinion.
> 
> I guess that sounds pretty reasonable to me, too.

I'm not sure the intent of my original bug report made it through
this discussion :-). I don't see why you'd always have to emit
debug info for every header file in every compilation unit.
Just emit debug info for types that are "used". The point of the
bug report was to say that the "this" variable should count
as "using" a type, and if a derived class is "used", then all its
base classes should be "used" as well (after all, there isn't
all that much difference between a base class and a member variable,
and you wouldn't leave out member variables just because they
weren't directly referenced would you?).

Of course I say this is total ignorance of how gcc decides to emit
debug info :-).