Add const

src/hb-object-private.h

@@ -63,7 +63,7 @@ typedef struct {
 #endif
 
 static HB_GNUC_UNUSED inline hb_bool_t /* always returns TRUE */
-_hb_object_debug_out (void *obj,
+_hb_object_debug_out (const void *obj,
 		      hb_reference_count_t *ref_count,
 		      const char *function)
 {