Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/log_android.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_ANDROID)
+#if defined(HOST_OS_ANDROID)
 
 #include "bin/log.h"
 
 #include <android/log.h>  // NOLINT
 #include <stdio.h>        // NOLINT
 
 namespace dart {
 namespace bin {
 
 // TODO(gram): We should be buffering the data and only outputting
@@ skipping 13 matching lines @@
   // (critical ones or not) if we print them to stdout/stderr.
   // We also log using android's logging system.
   vfprintf(stderr, format, args);
   fflush(stderr);
   __android_log_vprint(ANDROID_LOG_ERROR, "Dart", format, args);
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_ANDROID)
+#endif  // defined(HOST_OS_ANDROID)