Update vulkan headers

thirdparty/include/vulkan/vk_platform.h

@@ -2,19 +2,9 @@
 // File: vk_platform.h
 //
 /*
-** Copyright (c) 2014-2020 The Khronos Group Inc.
+** Copyright 2014-2021 The Khronos Group Inc.
 **
-** Licensed under the Apache License, Version 2.0 (the "License");
-** you may not use this file except in compliance with the License.
-** You may obtain a copy of the License at
-**
-**     http://www.apache.org/licenses/LICENSE-2.0
-**
-** Unless required by applicable law or agreed to in writing, software
-** distributed under the License is distributed on an "AS IS" BASIS,
-** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-** See the License for the specific language governing permissions and
-** limitations under the License.
+** SPDX-License-Identifier: Apache-2.0
 */
 
 
@@ -68,7 +58,9 @@ extern "C"
     #define VKAPI_PTR
 #endif
 
-#include <stddef.h>
+#if !defined(VK_NO_STDDEF_H)
+    #include <stddef.h>
+#endif // !defined(VK_NO_STDDEF_H)
 
 #if !defined(VK_NO_STDINT_H)
     #if defined(_MSC_VER) && (_MSC_VER < 1600)