Fix linking when dirauth module is disabled.

Bugfix on dcee4d4c9cc7d98e5ae8e913c73a3afc41753c64, bug not in any
released Tor.

src/or/config.c

@@ -3517,12 +3517,14 @@ options_validate(or_options_t *old_options, or_options_t *options,
       REJECT("Versioning authoritative dir servers must set "
              "Recommended*Versions.");
 
+#ifdef HAVE_MODULE_DIRAUTH
     char *t;
     /* Call these functions to produce warnings only. */
     t = format_recommended_version_list(options->RecommendedClientVersions, 1);
     tor_free(t);
     t = format_recommended_version_list(options->RecommendedServerVersions, 1);
     tor_free(t);
+#endif
 
     if (options->UseEntryGuards) {
       log_info(LD_CONFIG, "Authoritative directory servers can't set "