Add file header

Author: blaugold

pkgs/native_toolchain_c/test/cbuilder/testfiles/dynamically_linked/src/dynamically_linked.c

@@ -1,3 +1,7 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
 #include "add.h"
 
 int main() {