Add include of signal.h for signal() prototype.

usr.sbin/ypldap/ldapclient.c

@@ -34,6 +34,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <pwd.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>