swift234

Emit pointers to final overriders of member functions into
the metadata objects for classes.  This is currently only
done for methods defined in the main class body, and it's
(naturally) totally fragile, and it's screwed up in a
couple known ways w.r.t. generic classes:  there's no
thunking when the overrider differs by abstraction from
the overridden method, and methods on classes currently
expect to get all the type arguments passed directly
and thus will disagree in signature from members of
non-generic classes.  Also, of course, we're not using
any of this in the call infrastructure.  But it's progress.

Swift SVN r2901