[AST] PackArchetypes have concrete packs.

Add the recursive property.

Author: nate-chandler

lib/AST/Type.cpp

@@ -3703,8 +3703,9 @@ PackArchetypeType::PackArchetypeType(
     ArrayRef<ProtocolDecl *> ConformsTo, Type Superclass,
     LayoutConstraint Layout, PackShape Shape)
     : ArchetypeType(TypeKind::PackArchetype, Ctx,
-                    RecursiveTypeProperties::HasArchetype, InterfaceType,
-                    ConformsTo, Superclass, Layout, GenericEnv) {
+                    RecursiveTypeProperties::HasArchetype |
+                        RecursiveTypeProperties::HasConcretePack,
+                    InterfaceType, ConformsTo, Superclass, Layout, GenericEnv) {
   assert(InterfaceType->isParameterPack());
   *getTrailingObjects<PackShape>() = Shape;
 }