swift234

Runtime: part 1 of work to enable CoreData

Until we lock down the Swift ABI and ship with the OS, we need to be resilient
in the face of ObjC dynamic subclassing and OS changes. In practice, this means
that we need to have a swift runtime ABI to read the isa out of objects. I've
added it as of r. See: swift_getClassMetadata()

We can and will optimize swift_getClassMetadata into a single instruction once
we lockdown our ABI and ship with the OS.

See also: <rdar://problem/16735599>

Swift SVN r16889