swift234

[swift2objc] Print arbitrary class metatypes as "SWIFT_METATYPE(MyClass)"

...and then define SWIFT_METATYPE(X) as a macro for "Class", because
Objective-C doesn't have a way to constrain class types to a certain
hierarchy.

With this change, we should handle every type that makes it through the
@objc validator today.

Swift SVN r12190