constexpr month_weekday_last(const chrono::month& m,
const chrono::weekday_last& wdl) noexcept;
constexpr chrono::month month() const noexcept;
constexpr chrono::weekday_last weekday_last() const noexcept;
constexpr bool ok() const noexcept;
constexpr bool operator==(const month_weekday_last& x, const month_weekday_last& y) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const month_weekday_last& mwdl);