Turn //mojo/public/cpp/bindings and //mojo/public/cpp/system into components

mojo/public/interfaces/bindings/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../tools/bindings/mojom.gni")
 
 mojom("bindings") {
   sources = [
     "interface_control_messages.mojom",
     "pipe_control_messages.mojom",
   ]
+
+  export_class_attribute = "MOJO_CPP_BINDINGS_EXPORT"
+  export_define = "MOJO_CPP_BINDINGS_IMPLEMENTATION"
+  export_header = "mojo/public/cpp/bindings/bindings_export.h"
 }