Function try_lock_tail

uspace/lib/cpp/include/__bits/thread/mutex.hpp:444–450

    {
        template<class L>
        int try_lock_tail(int idx, L& l)
        {
            if (!l.try_lock())
                return idx;
            else
                return -1;
        }

        template<class L1, class... L2>
        int try_lock_tail(int idx, L1& l1, L2&... ls)