Rename TARGET_OS_* to HOST_OS_*.

runtime/bin/secure_socket_ios.cc

 // Copyright (c) 2016, 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) && !defined(DART_IO_SECURE_SOCKET_DISABLED)
 
 #include "platform/globals.h"
-#if TARGET_OS_IOS
+#if HOST_OS_IOS
 
 #include "bin/secure_socket.h"
 #include "bin/secure_socket_ios.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/syslimits.h>
 #include <stdio.h>
 #include <string.h>
@@ skipping 1476 matching lines @@
     Log::PrintErr("ProcessWritePlaintextBuffer: requested: %ld, written: %ld\n",
                   length, bytes);
   }
   *bytes_processed = static_cast<intptr_t>(bytes);
   return status;
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // TARGET_OS_IOS
+#endif  // HOST_OS_IOS
 
 #endif  // !defined(DART_IO_SECURE_SOCKET_DISABLED)