common: fix unused variable warning

The saved_data variable in uv_loop_close() is only used when
NDEBUG is defined. This commit makes the variable declaration
depend on NDEBUG as well.

PR-URL: https://github.com/libuv/libuv/pull/1093
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

src/uv-common.c

@@ -613,7 +613,9 @@ uv_loop_t* uv_loop_new(void) {
 int uv_loop_close(uv_loop_t* loop) {
   QUEUE* q;
   uv_handle_t* h;
+#ifndef NDEBUG
   void* saved_data;
+#endif
 
   if (!QUEUE_EMPTY(&(loop)->active_reqs))
     return UV_EBUSY;