Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/file_win.cc

Index: runtime/bin/file_win.cc
diff --git a/runtime/bin/file_win.cc b/runtime/bin/file_win.cc
index 9255ca2ad72f22bb22de263d8a83956850530c3e..883b911a13b0f571995859177f61852903d562bc 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
-#if defined(TARGET_OS_WINDOWS)
+#if defined(HOST_OS_WINDOWS)
 
 #include "bin/file.h"
 
@@ -831,4 +831,4 @@ File::Identical File::AreIdentical(const char* file_1, const char* file_2) {
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_WINDOWS)
+#endif  // defined(HOST_OS_WINDOWS)