Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/file_system_watcher_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.
 
 #if !defined(DART_IO_DISABLED)
 
 #include "platform/globals.h"
-#if defined(TARGET_OS_LINUX)
+#if defined(HOST_OS_LINUX)
 
 #include "bin/file_system_watcher.h"
 
 #include <errno.h>        // NOLINT
 #include <sys/inotify.h>  // NOLINT
 
 #include "bin/fdutils.h"
 #include "bin/socket.h"
 #include "platform/signal_blocker.h"
 
@@ skipping 121 matching lines @@
     }
     offset += kEventSize + e->len;
   }
   ASSERT(offset == bytes);
   return events;
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_LINUX)
+#endif  // defined(HOST_OS_LINUX)
 
 #endif  // !defined(DART_IO_DISABLED)