https://bugs.gentoo.org/870949
--- a/sig_pause.c
+++ b/sig_pause.c
@@ -1,5 +1,9 @@
 /* Public domain. */
 
+#ifndef _XOPEN_SOURCE
+#define _XOPEN_SOURCE 500
+#endif
+
 #include <signal.h>
 #include "sig.h"
 #include "hassgprm.h"