vcall slots and destructors

[Jason Merrill]

I recently noticed that g++ allocates to vcall slots for a virtual
destructor, one for each of the variants that go into the vtable.  It seems
to me that we only need one, since they can't be overridden separately.

Also, is it explicitly stated anywhere that the VTT parm comes right after
'this'?  That makes the most sense to me, but I don't see it written down
anywhere.

Jason