swift234

IRGen: Implement type info for class-bounded archetypes.

Split ArchetypeTypeInfo into ClassBoundedArchetypeTypeInfo, for class-bounded archetypes, and OpaqueArchetypeTypeInfo, for fully generalized archetypes (the existing case). ClassBoundedArchetypeTypeInfo is represented using a single refcounted ObjCPointer. Implement abstraction remapping from class instances to class-bounded archetypes and back, and from class-bounded archetypes to non-class-bounded and back.

Witness tables are still generated only for opaque archetypes, so method calls on class-bounded archetypes won't work just yet.

Swift SVN r5569