third_party/protobuf: Update to HEAD (83d681ee2c)

third_party/protobuf/csharp/src/Google.Protobuf/FrameworkPortability.cs

 #region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
@@ skipping 29 matching lines @@
     /// </summary>
     internal static class FrameworkPortability
     {
         // The value of RegexOptions.Compiled is 8. We can test for the presence at
         // execution time using Enum.IsDefined, so a single build will do the right thing
         // on each platform. (RegexOptions.Compiled isn't supported by PCLs.)
         internal static readonly RegexOptions CompiledRegexWhereAvailable =
             Enum.IsDefined(typeof(RegexOptions), 8) ? (RegexOptions)8 : RegexOptions.None;
     }
 }