Move exit from the builtin library to dart:io.

runtime/bin/process.dart

 // 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.
 
+/** Exit the Dart VM process with the given [status] code. */
+void exit(int status) {
+  if (status is !int) {
+    throw new IllegalArgumentException("int status expected");
+  }
+  _exit(status);
+}
+
 /**
  * [Process] is used to start new processes using the static
  * [start] and [run] methods.
  */
 class Process {
   /**
    * Starts a process running the [executable] with the specified
    * [arguments]. Returns a [Process] instance that can be used to
    * interact with the process.
    *
@@ skipping 212 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;
 }