Add missing STARPU_HAVE_ATOMIC_EXCHANGE_N macro in starpu_config.h

include/starpu_config.h.in

@@ -152,6 +152,7 @@
 #undef STARPU_HAVE_SYNC_FETCH_AND_OR
 #undef STARPU_HAVE_SYNC_LOCK_TEST_AND_SET
 #undef STARPU_HAVE_SYNC_SYNCHRONIZE
+#undef STARPU_HAVE_ATOMIC_EXCHANGE_N
 
 #undef STARPU_DEVEL
 #undef STARPU_MODEL_DEBUG