Tru64 diff does support "diff foo /dev/null",

replace with "diff foo - < /dev/null"

tests/scripts/test005-modrdn

@@ -147,7 +147,7 @@ if test $RC != 0 ; then
 	echo "ldapsearch failed ($RC)!"
 	exit $RC
 fi
-$CMP $SEARCHOUT /dev/null > $CMPOUT
+$CMP $SEARCHOUT - < /dev/null > $CMPOUT
 if test $? != 0 ; then
 	echo "failure: ldapsearch found attribute that was to be removed!"
 	kill -HUP $PID