Guard definition of TIPC_SUB_CANCEL with an #ifdef.

Modules/socketmodule.c

@@ -4591,7 +4591,10 @@ init_socket(void)
 	/* for subscriptions */
 	PyModule_AddIntConstant(m, "TIPC_SUB_PORTS", TIPC_SUB_PORTS);
 	PyModule_AddIntConstant(m, "TIPC_SUB_SERVICE", TIPC_SUB_SERVICE);
-     /* PyModule_AddIntConstant(m, "TIPC_SUB_CANCEL", TIPC_SUB_CANCEL); XXX This var is missing on gcc (GCC) 4.1.1 (Gentoo 4.1.1) and it breaks the build */
+#ifdef TIPC_SUB_CANCEL
+	/* doesn't seem to be available everywhere */
+	PyModule_AddIntConstant(m, "TIPC_SUB_CANCEL", TIPC_SUB_CANCEL);
+#endif
 	PyModule_AddIntConstant(m, "TIPC_WAIT_FOREVER", TIPC_WAIT_FOREVER);
 	PyModule_AddIntConstant(m, "TIPC_PUBLISHED", TIPC_PUBLISHED);
 	PyModule_AddIntConstant(m, "TIPC_WITHDRAWN", TIPC_WITHDRAWN);