[RFA/stabs reader] Fix v3 duplicate constructors problem

[Joe Buck]

> 
> 
> Jason Merrill <jason@redhat.com> writes:
> > Constructors and destructors have traditionally had a special calling
> > convention.  Though I suppose that as of v3, we've gone to clones rather
> > than extra hidden parameters, so it would be more feasible to allow users
> > to call them directly from the debugger.  In any case, it needs some sort
> > of special handling.
> 
> Wouldn't it be reasonable for GDB to support `new' expressions?

Yes, if the gdb user can call placement new, s/he can call a constructor
and place an object whereever desired.  Something like

(gdb) call new(ptr) SomeClass(1, "Hello")