swift234

[PrintAsObjC] Add objc_complete_definition attribute to generated @interfaces.

This is using the compatibility macro SWIFT_CLASS, so older Clangs can still
parse a generated header on its own. This will only be interesting in a
mixed-source target, where we may need to merge a forward declaration with
a Swift-generated @interface. (See <rdar://problem/16076729>.)

Swift SVN r14411