Rename TARGET_OS_* to HOST_OS_*.

runtime/platform/signal_blocker.h

 // 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.
 
 #ifndef RUNTIME_PLATFORM_SIGNAL_BLOCKER_H_
 #define RUNTIME_PLATFORM_SIGNAL_BLOCKER_H_
 
 #include "platform/globals.h"
 #include "platform/assert.h"
 
-#if defined(TARGET_OS_WINDOWS)
+#if defined(HOST_OS_WINDOWS)
 #error Do not include this file on Windows.
 #endif
 
 #include <pthread.h>
 #include <signal.h>  // NOLINT
 
 namespace dart {
 
 class ThreadSignalBlocker {
  public:
@@ skipping 85 matching lines @@
     } while ((__result == -1L) && (errno == EINTR));                           \
     __result;                                                                  \
   })
 
 #define VOID_TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(expression)                  \
   (static_cast<void>(TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(expression)))
 
 }  // namespace dart
 
 #endif  // RUNTIME_PLATFORM_SIGNAL_BLOCKER_H_