Why don't we just FIX the damn vthunk problem?

[Jason Merrill]

OK, I see the problem.  It hits us when the most derived class is compiled
with an old compiler.

Going back to your earlier idea, I think it would be better to keep in_chrg
and have the vtable list as an additional parameter, for two reasons:

 1) It's also used to control calling op delete in dtors.
 2) If we do, the binary compatibility wrappers can DTRT (or at least as R
    as the current code) instead of aborting.

Jason