Rename TARGET_OS_* to HOST_OS_*.

runtime/platform/utils.h

 // 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.
 
 #ifndef RUNTIME_PLATFORM_UTILS_H_
 #define RUNTIME_PLATFORM_UTILS_H_
 
 #include "platform/assert.h"
 #include "platform/globals.h"
 
@@ skipping 190 matching lines @@
   // represent anything in the range -2^53 ... 2^53.
   static bool IsJavascriptInt(int64_t value) {
     return ((-0x20000000000000LL <= value) && (value <= 0x20000000000000LL));
   }
 
   static char* StrError(int err, char* buffer, size_t bufsize);
 };
 
 }  // namespace dart
 
-#if defined(TARGET_OS_ANDROID)
+#if defined(HOST_OS_ANDROID)
 #include "platform/utils_android.h"
-#elif defined(TARGET_OS_FUCHSIA)
+#elif defined(HOST_OS_FUCHSIA)
 #include "platform/utils_fuchsia.h"
-#elif defined(TARGET_OS_LINUX)
+#elif defined(HOST_OS_LINUX)
 #include "platform/utils_linux.h"
-#elif defined(TARGET_OS_MACOS)
+#elif defined(HOST_OS_MACOS)
 #include "platform/utils_macos.h"
-#elif defined(TARGET_OS_WINDOWS)
+#elif defined(HOST_OS_WINDOWS)
 #include "platform/utils_win.h"
 #else
 #error Unknown target os.
 #endif
 
 #endif  // RUNTIME_PLATFORM_UTILS_H_