[Issue 21783] Add `if` as an operator

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21783

--- Comment #2 from anonymous4 <dfj1esp02 at sneakemail.com> ---
bool conditional(bool c, bool check)
{
    return c?check:true;
}

    void divMod(int a, int b, int q, int r)
        in (b > 0)
        out (; conditional(a < 0, q <= 0))
        out (; conditional(a > 0, q >= 0))
        out (; conditional(a < 0, r <= 0))
        out (; conditional(a > 0, r >= 0))

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