In IRGen, @autoreleased return values are always converted to +1 by
calling objc_retainAutoreleasedReturnValue(), so a partial application
thunk cannot have a result with @autoreleased convention. Just turn
it into @owned instead, since that's what it is, using similar logic
as the @unowned_inner_pointer => @unowned case.
Fixes <rdar://problem/24805609>.
Previously, we attempted to infer @objc-ness based on conformance, but
doing so is fraught with ordering dependencies, and just doesn't work
in the general case. Among other crimes, this allowed us to
retroactively mark a non-@objc method from an imported module as
@objc... even though nobody would ever then emit the @objc entry
points for it.
Fixes the rest of rdar://problem/18383574.
Swift SVN r24831
Just injecting a new protocol descriptor into an already-running ObjC runtime isn't a good idea, since the runtime might have already canonized the protocol somewhere else, and it won't recognize that classes conform to protocols it doesn't know about.
Swift SVN r23313
