Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/thread_interrupter_android.cc

 // 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.
 
 #include "platform/globals.h"
-#if defined(TARGET_OS_ANDROID)
+#if defined(HOST_OS_ANDROID)
 
 #include <sys/syscall.h>  // NOLINT
 #include <errno.h>        // NOLINT
 
 #include "vm/flags.h"
 #include "vm/os.h"
 #include "vm/profiler.h"
 #include "vm/signal_handler.h"
 #include "vm/thread_interrupter.h"
 
@@ skipping 52 matching lines @@
 
 
 void ThreadInterrupter::RemoveSignalHandler() {
   SignalHandler::Remove();
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_ANDROID)
+#endif  // defined(HOST_OS_ANDROID)