Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/thread_fuchsia.cc

 // Copyright (c) 2016, 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_FUCHSIA)
+#if defined(HOST_OS_FUCHSIA)
 
 #include "bin/thread.h"
 #include "bin/thread_fuchsia.h"
 
 #include <errno.h>         // NOLINT
 #include <sys/resource.h>  // NOLINT
 #include <sys/time.h>      // NOLINT
 
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 297 matching lines @@
 
 void Monitor::NotifyAll() {
   // TODO(iposva): Do we need to track lock owners?
   int result = pthread_cond_broadcast(data_.cond());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_FUCHSIA)
+#endif  // defined(HOST_OS_FUCHSIA)