Ensure CC entries always marked, add missing WB

Previously we were issuing writebarriers for each cc, but were missing
the cme.

We also need to avoid it being possible to run GC after we've copied the
values into the allocated array, but before they're visible in the
object.

Author: jhawthorn

vm_method.c

@@ -136,17 +136,19 @@ rb_vm_cc_table_create(size_t capa)
 static enum rb_id_table_iterator_result
 vm_cc_table_dup_i(ID key, VALUE old_ccs_ptr, void *data)
 {
+    VALUE new_table = (VALUE)data;
     struct rb_class_cc_entries *old_ccs = (struct rb_class_cc_entries *)old_ccs_ptr;
     size_t memsize = vm_ccs_alloc_size(old_ccs->capa);
-    struct rb_class_cc_entries *new_ccs = ruby_xmalloc(memsize);
+    struct rb_class_cc_entries *new_ccs = ruby_xcalloc(1, memsize);
+    rb_managed_id_table_insert(new_table, key, (VALUE)new_ccs);
+
     memcpy(new_ccs, old_ccs, memsize);
 
 #if VM_CHECK_MODE > 0
     new_ccs->debug_sig = ~(VALUE)new_ccs;
 #endif
 
-    VALUE new_table = (VALUE)data;
-    rb_managed_id_table_insert(new_table, key, (VALUE)new_ccs);
+    RB_OBJ_WRITTEN(new_table, Qundef, (VALUE)new_ccs->cme);
     for (int index = 0; index < new_ccs->len; index++) {
         RB_OBJ_WRITTEN(new_table, Qundef, new_ccs->entries[index].cc);
     }