Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/directory_win.cc

Index: runtime/bin/directory_win.cc
diff --git a/runtime/bin/directory_win.cc b/runtime/bin/directory_win.cc
index e9a5be999f4cc47cbae6db3ac946f31a4cce7f61..df82c11d87fdf701c7d5ae0091ff5846462ed015 100644
--- a/runtime/bin/directory_win.cc
+++ b/runtime/bin/directory_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/directory.h"
 #include "bin/file.h"
@@ -510,4 +510,4 @@ bool Directory::Rename(const char* path, const char* new_path) {
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_WINDOWS)
+#endif  // defined(HOST_OS_WINDOWS)