Do not let sysctl abort due a missed file or directory under /proc.

Include signal.h for compiling w.

Signed-off-by: Werner Fink <werner@suse.de>

w.c

@@ -15,6 +15,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>