libvpx: Pull from upstream

source/libvpx/warnings.c

 /*
  *  Copyright (c) 2013 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 36 matching lines @@
   new_node->warning_string = warning_string;
   new_node->next_warning = NULL;
 
   while (*node != NULL)
     node = &(*node)->next_warning;
 
   *node = new_node;
 }
 
 static void free_warning_list(struct WarningList *warning_list) {
-  struct WarningListNode *node = warning_list->warning_node;
   while (warning_list->warning_node != NULL) {
-    node = warning_list->warning_node->next_warning;
-    free(warning_list->warning_node);
-    warning_list->warning_node = node;
+    struct WarningListNode *const node = warning_list->warning_node;
+    warning_list->warning_node = node->next_warning;
+    free(node);
   }
 }
 
 static int continue_prompt(int num_warnings) {
   int c;
   fprintf(stderr,
           "%d encoder configuration warning(s). Continue? (y to continue) ",
           num_warnings);
   c = getchar();
   return c == 'y';
@@ skipping 35 matching lines @@
     warn(warning->warning_string);
   }
 
   free_warning_list(&warning_list);
 
   if (num_warnings) {
     if (!disable_prompt && !continue_prompt(num_warnings))
       exit(EXIT_FAILURE);
   }
 }