Add UNREF macro if not tracing refs (see UNREF function in object.c).
diff --git a/Include/object.h b/Include/object.h
index 7147339..dcfdfb4 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -191,6 +191,7 @@
 
 #ifndef TRACE_REFS
 #define DELREF(op) (*(op)->ob_type->tp_dealloc)((object *)(op))
+#define UNREF(op) /*empty*/
 #endif
 
 #ifdef REF_DEBUG