conditionally declare fctx

lib/dns/resolver.c

@@ -8939,6 +8939,9 @@ rctx_resend(respctx_t *rctx, dns_adbaddrinfo_t *addrinfo) {
  */
 static void
 rctx_next(respctx_t *rctx) {
+#ifdef WANT_QUERYTRACE
+	fetchctx_t *fctx = rctx->fctx;
+#endif
 	isc_result_t result;
 
 	FCTXTRACE("nextitem");