Commented out export of missing CRML source file to avoid build error.
There are no known side effects of this file being missing, so this seems a reasonable way to avoid the build error.
// Copyright (C) 2003, Fernando Luis Cacciola Carballal.
//
// Use, modification, and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/lib/optional for documentation.
//
// You are welcome to contact the author at:
// fernando_cacciola@hotmail.com
//
#ifndef BOOST_OPTIONAL_FLC_19NOV2002_HPP
#define BOOST_OPTIONAL_FLC_19NOV2002_HPP
#include "boost/optional/optional.hpp"
#endif