[Bug c++/84435] -Wliteral-suffix warns on a using-directive

[mferoldif at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84435

--- Comment #1 from Mário Feroldi <mferoldif at gmail dot com> ---
Note that the following `foo`'s variant doesn't make the warning go away:

    int foo(E e)
    {
        (e == E::A || e == E::B || e == E::C) ? void() :
__builtin_unreachable();
        switch (e)
        {
            case E::A: return 0;
            case E::B: return 1;
            case E::C: return 2;
        }
    }