update SPIRV-CROSS to latest

SHA: ff61890722a91e97c44940494be5b6eed0d5ff5b

third_party/spirv-cross/spirv_cpp.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015-2020 Arm Limited
+ * Copyright 2015-2021 Arm Limited
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,6 +14,13 @@
  * limitations under the License.
  */
 
+/*
+ * At your option, you may choose to accept this material under either:
+ *  1. The Apache License, Version 2.0, found at <http://www.apache.org/licenses/LICENSE-2.0>, or
+ *  2. The MIT License, found at <http://opensource.org/licenses/MIT>.
+ * SPDX-License-Identifier: Apache-2.0 OR MIT.
+ */
+
 #include "spirv_cpp.hpp"
 
 using namespace spv;