avoid complaints about _BSD_SOURCE on ubuntu
diff --git a/skeletons/asn_system.h b/skeletons/asn_system.h
index ce46242..fa8cf11 100644
--- a/skeletons/asn_system.h
+++ b/skeletons/asn_system.h
@@ -12,6 +12,10 @@
 #include "config.h"
 #endif
 
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE 1
+#endif
+
 #ifndef _BSD_SOURCE
 #define _BSD_SOURCE /* for snprintf() on some linux systems  */
 #endif