[dart:io][windows] Set the last error when a signal is unsupported

runtime/bin/process_win.cc

 // Copyright (c) 2012, 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.
 
 #if !defined(DART_IO_DISABLED)
 
 #include "platform/globals.h"
 #if defined(HOST_OS_WINDOWS)
 
 #include "bin/process.h"
@@ skipping 965 matching lines @@
       return CTRL_C_EVENT;
     default:
       return -1;
   }
 }
 
 
 intptr_t Process::SetSignalHandler(intptr_t signal) {
   signal = GetWinSignal(signal);
   if (signal == -1) {
+    SetLastError(ERROR_NOT_SUPPORTED);
     return -1;
   }
 
   // Generate a unique pipe name for the named pipe.
   wchar_t pipe_name[kMaxPipeNameSize];
   int status = GenerateNames<1>(&pipe_name);
   if (status != 0) {
     return status;
   }
 
@@ skipping 54 matching lines @@
   }
   delete handler;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_WINDOWS)
 
 #endif  // !defined(DART_IO_DISABLED)