add SA_NOMASK alias for SA_NODEFER with _GNU_SOURCE
diff --git a/include/signal.h b/include/signal.h
index 2e621ac..1b58908 100644
--- a/include/signal.h
+++ b/include/signal.h
@@ -102,6 +102,7 @@
 #ifdef _GNU_SOURCE
 typedef void (*sighandler_t)(int);
 void (*bsd_signal(int, void (*)(int)))(int);
+#define SA_NOMASK SA_NODEFER
 #endif
 
 #include <bits/signal.h>