swift234

Implement runtime checking for super-to-archetype casts, finishing <rdar://problem/12768631>.

Introduce a new swift_dynamicCast pair that take in a general metatype
pointer, rather than the more specific class-metatype pointer used for
class downcasts, and grab the class out of that general metatype
pointer, which may actually be an Objective-C wrapper. This is
slightly slower, but it works for the super-to-archetype cases like
T(an_NSObject), where T can have either kind of metadata.

NSTypedArray<T> is actually run-time type checked now, yay!


Swift SVN r3564