configure: require TLS1.3 support in gnutls

Before enabling NTS support, explicitly check for TLS1.3 support in
gnutls, which is required by NTS.

diff --git a/configure b/configure
index 691d08ee93a77e49a7157a54b213abb7637938c2..d13b85ee71a6a1808dc3740918cece1c3c2dcdf6 100755 (executable)
--- a/configure
+++ b/configure
@@ -974,7 +974,7 @@ if [ $feat_ntp = "1" ] && [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
   test_link="`pkg_config --libs gnutls`"
   if test_code 'gnutls' 'gnutls/gnutls.h' \
     "$test_cflags" "$test_link" '
-      return gnutls_init(NULL, 0) +
+      return gnutls_init(NULL, 0) + GNUTLS_TLS1_3 +
         gnutls_priority_init2(NULL, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
         gnutls_prf_rfc5705(NULL, 0, "", 0, "", 16, NULL);'
   then