Patch from: https://github.com/void-linux/void-packages/commit/0f6da07

--- a/utmp.c
+++ b/utmp.c
@@ -30,6 +30,7 @@
 
 #include "utmp.h"
 
+#include <signal.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>