Add support for detecting ED25519 support in GnuTLS

configure.ac

@@ -113,20 +113,20 @@ AM_CONDITIONAL([FAST_PARSER], [test "$enable_fastparser" = "yes"])
 # GnuTLS crypto backend
 PKG_CHECK_MODULES([gnutls], [gnutls >= 3.3 nettle], [
     save_CFLAGS=$CFLAGS
+    save_LIBS=$LIBS
     CFLAGS="$CFLAGS $gnutls_CFLAGS"
+    LIBS="$LIBS $gnutls_LIBS"
     AC_CHECK_HEADERS([nettle/version.h])
-    CFLAGS=$save_CFLAGS
 
-    save_LIBS=$LIBS
-    LIBS="$LIBS $gnutls_LIBS"
     AC_CHECK_FUNC([gnutls_pkcs11_copy_pubkey], [enable_pkcs11=yes], [enable_pkcs11=no])
     AS_IF([test "$enable_pkcs11" = yes],
         [AC_DEFINE([ENABLE_PKCS11], [1], [PKCS #11 support available])])
 
-    AC_CHECK_DEFINE([$gnutls_CFLAGS], [GNUTLS_PK_EDDSA_ED25519], [enable_ed25519=yes], [enable_ed25519=no])
+    AC_CHECK_DECL([GNUTLS_PK_EDDSA_ED25519], [enable_ed25519=yes], [enable_ed25519=no], [#include <gnutls/gnutls.h>])
     AS_IF([test "$enable_ed25519" = yes],
         [AC_DEFINE([HAVE_ED25519], [1], [GnuTLS ED25519 support available])])
 
+    CFLAGS=$save_CFLAGS
     LIBS=$save_LIBS
 ])
 
@@ -569,6 +569,7 @@ result_msg_base="  $PACKAGE $VERSION
     Utilities with Dnstap:  ${opt_dnstap}
     Systemd integration:    ${enable_systemd}
     PKCS #11 support:       ${enable_pkcs11}
+    ED25519 support:        ${enable_ed25519}
     Code coverage:          ${enable_code_coverage}
     Sanitizer:              ${with_sanitize}
     LibFuzzer:              ${libfuzzer_LIBS}"