fix objc_resolve_class_links to actually rescan the unresolved list

It looks like this was the initial intent of 4ea82e1, but as implemented
it would still only scan the unresolved class list once. Since
unresolved_class_list represents the head and classes are pushed onto
the head, any classes added to the resolution list after resolution
started would be skipped.

class_table.c

@@ -258,10 +258,10 @@ PRIVATE BOOL objc_resolve_class(Class cls)
 PRIVATE void objc_resolve_class_links(void)
 {
 	LOCK_RUNTIME_FOR_SCOPE();
-	Class class = unresolved_class_list;
 	BOOL resolvedClass;
 	do
 	{
+		Class class = unresolved_class_list;
 		resolvedClass = NO;
 		while ((Nil != class))
 		{