error_code, when converted to std::error_code and back, doesn't roundtrip

[pdimov]

As reported by @ned14 in https://wandbox.org/permlink/FateL4bRSowzQHDM.

#include <boost/asio.hpp>
#include <system_error>

int main(void)
{
    if(boost::system::error_code(std::error_code(boost::system::error_code(boost::asio::error::eof))) != boost::asio::error::eof)
    {
        abort();
    }
    return 0;
}