Mark the class on orphan call caches

"super" CC's are "orphans", meaning there is no class CC table that
points at them.  Since they are orphans, we should mark the class
reference so that if the cache happens to be used, the class will still
be alive

imemo.c

@@ -316,6 +316,7 @@ rb_imemo_mark_and_move(VALUE obj, bool reference_updating)
         else {
             if (vm_cc_super_p(cc) || vm_cc_refinement_p(cc)) {
                 rb_gc_mark_movable((VALUE)cc->cme_);
+                rb_gc_mark_movable((VALUE)cc->klass);
             }
         }