Extend the mDNS package with a native extension used on Mac OS

src/pkg/mdns/mdns_extension_linux.cc

Index: src/pkg/mdns/mdns_extension_linux.cc
diff --git a/src/pkg/mdns/mdns_extension_linux.cc b/src/pkg/mdns/mdns_extension_linux.cc
new file mode 100644
index 0000000000000000000000000000000000000000..9ab4d2b48b4d742387af38d7c5f308c5b31d1bf5
--- /dev/null
+++ b/src/pkg/mdns/mdns_extension_linux.cc
@@ -0,0 +1,20 @@
+// Copyright (c) 2015, the Fletch 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.md file.
+
+#if defined(FLETCH_TARGET_OS_LINUX)
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "include/dart_api.h"
+#include "include/dart_native_api.h"
+
+#include "mdns_extension.h"
+
+// Dummy implementation for Linux.
+void HandleLookup(Dart_Port port_id, char* adress) {}
+
+#endif