Skip over any CallContext we encounter - future Rakudo refactors will…

… avoid the need for this hack in the long run. And...tada! We successfully serialize CORE.setting, producing 1393664 bytes of serialized data with 10578 strings in the string heap. Sadly, we then explode in the optimizer...

src/6model/serialization.c

@@ -411,6 +411,11 @@ void write_ref_func(PARROT_INTERP, SerializationWriter *writer, PMC *ref) {
          * we just drop it. */
         discrim = REFVAR_VM_NULL;
     }
+    else if (ref->vtable->base_type == enum_class_CallContext) {
+        /* XXX This is a hack for Rakudo's sake; it keeps a CallContext around in
+         * the lexpad, for no really good reason. */
+        discrim = REFVAR_VM_NULL;
+    }
     else if (ref->vtable->base_type == smo_id) {
         discrim = REFVAR_OBJECT;
     }