Add a nacl module args file.

This is being added to the nacl directory and the Chrome one needs to match.

TBR=bradnelson@chromium.org

Review URL: https://codereview.chromium.org/1198633002

Cr-Original-Commit-Position: refs/heads/master@{#335364}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 53e14ad309ecde58d21f261f9a8297a98f7ae4f5

module_args/nacl.gni

@@ -0,0 +1,6 @@
+# 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.
+
+# Override nacl's build directory.
+nacl_shared_build_dir = "//build"