Fix patch file return types

sdk/lib/io/process.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 // TODO(ager): The only reason for this class is that we
 // cannot patch a top-level at this point.
 class _ProcessUtils {
-  external static _exit(int status);
-  external static _setExitCode(int status);
-  external static _sleep(int millis);
+  external static void _exit(int status);
+  external static void _setExitCode(int status);
+  external static void _sleep(int millis);
   external static int _pid(Process process);
 }
 
 /**
  * Exit the Dart VM process immediately with the given [status] code.
  *
  * This does not wait for any asynchronous operations to terminate. Using
  * [exit] is therefore very likely to lose data.
  */
 void exit(int status) {
@@ skipping 267 matching lines @@
   /**
    * Contains the system message for the process exception if any.
    */
   final String message;
 
   /**
    * Contains the OS error code for the process exception if any.
    */
   final int errorCode;
 }