Adapt error messages in tests/scripts/list-*
diff --git a/tests/scripts/list-enum-consts.pl b/tests/scripts/list-enum-consts.pl
index 4e0baec..bbb9490 100755
--- a/tests/scripts/list-enum-consts.pl
+++ b/tests/scripts/list-enum-consts.pl
@@ -6,6 +6,8 @@
 use utf8;
 use open qw(:std utf8);
 
+-d 'include/mbedtls' or die "$0: must be run from root\n";
+
 @ARGV = <include/mbedtls/*.h>;
 
 my @consts;