Class not_isempty

src/backward.h:3811–3816

    // and define this one here because C++98 is not happy with local defined
    // struct passed to template functions, fuuuu.
    struct not_isempty {
        bool operator()(const lines_t::value_type& p)
        {
            return !(std::find_if(p.second.begin(), p.second.end(), not_isspace()) == p.second.end());
        }
    };

    void swap(SourceFile& b) { _file.swap(b._file); }