Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/os_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.
 
 #include "vm/globals.h"
-#if defined(TARGET_OS_WINDOWS)
+#if defined(HOST_OS_WINDOWS)
 
 #include "vm/os.h"
 
 #include <malloc.h>   // NOLINT
 #include <process.h>  // NOLINT
 #include <psapi.h>    // NOLINT
 #include <time.h>     // NOLINT
 
 #include "platform/utils.h"
 #include "platform/assert.h"
@@ skipping 432 matching lines @@
 void OS::Exit(int code) {
   // TODO(zra): Remove once VM shuts down cleanly.
   private_flag_windows_run_tls_destructors = false;
   // On Windows we use ExitProcess so that threads can't clobber the exit_code.
   // See: https://code.google.com/p/nativeclient/issues/detail?id=2870
   ::ExitProcess(code);
 }
 
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_WINDOWS)
+#endif  // defined(HOST_OS_WINDOWS)