, "boost::unsupported_thread_option")            {            }            unsupported_thread_option( int ev, const char * what_arg )            : base_type(ev, what_arg)            {            }            unsupported_thread_option( int ev, const std::string & what_arg )            : base_type(ev, what_arg)            {            }        };        class BOOST_SYMBOL_VISIBLE 