swift234

Runtime: Fix logic inversion in objc_rootWeakRetained (which is really UnownedRetain).

We want to initialize the side weak reference the first time we retain a new unowned reference, not reinitialize the weak reference every time we retain it. Unowned @objc references are still racy, but this fixes the obvious brokenness behind <rdar://problem/17623813>.

Swift SVN r21074