Use ExitProcess on Windows.

runtime/bin/platform_macos.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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include <mach-o/dyld.h>
 #include <sys/types.h>
 #include <sys/sysctl.h>
@@ skipping 102 matching lines @@
   if (_NSGetExecutablePath(path, &path_size) != 0) {
     free(path);
     return NULL;
   }
   // Return the canonical path as the returned path might contain symlinks.
   char* canon_path = File::GetCanonicalPath(path);
   free(path);
   return canon_path;
 }
 
+void Platform::Exit(int exit_code) {
+  exit(exit_code);
+}
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)