Make _PyObject_GC_UnTrack do nothing if WITH_CYCLE_GC is not defined.
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index ed25bd4..d98e6a1 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -819,9 +819,11 @@
 void
 _PyObject_GC_UnTrack(PyObject *op)
 {
+#ifdef WITH_CYCLE_GC
 	PyGC_Head *gc = AS_GC(op);
 	if (gc->gc.gc_next != NULL)
 		_PyObject_GC_UNTRACK(op);
+#endif
 }
 
 PyObject *