Header sys/types.h is needed for id_t

Patch reported as bug upstream:
http://bugzilla.sudo.ws/show_bug.cgi?id=711

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>

diff -purN sudo-1.8.14p3.orig/include/sudo_util.h sudo-1.8.14p3/include/sudo_util.h
--- sudo-1.8.14p3.orig/include/sudo_util.h	2015-07-22 14:22:49.000000000 +0200
+++ sudo-1.8.14p3/include/sudo_util.h	2015-08-01 09:35:15.077909614 +0200
@@ -23,6 +23,8 @@
 # include "compat/stdbool.h"
 #endif /* HAVE_STDBOOL_H */
 
+#include <sys/types.h>
+
 /*
  * Macros for operating on struct timeval.
  */