Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/thread_interrupter_linux.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_LINUX)
+#if defined(HOST_OS_LINUX)
 
 #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"
 
 namespace dart {
@@ skipping 48 matching lines @@
 }
 
 
 void ThreadInterrupter::RemoveSignalHandler() {
   SignalHandler::Remove();
 }
 
 
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_LINUX)
+#endif  // defined(HOST_OS_LINUX)