Implement first D-specific optimization pass: -simplify-drtcalls. It uses the machinery of the standard -simplify-libcalls pass, but optimizes calls to the D runtime instead of calls to C libraries. At the moment, these optimizations are implemented by this pass: - Avoid the runtime call for `arr.length = newlen` if it can determine that the new length isn't longer than the old one. - Ditto for `cast(T[]) arr` if it will clearly always succeed. (e.g. if the length of the original array is zero, or if the old element size is a multiple of the new element size)

module tangotests.switch3;

void main()
{
    int i = 2;

    switch(i)
    {
        case 0,1,4,5,6,7,8,9:
            assert(0);
        case 2:
            return;
        case 3:
        {
            i++;
            case 11:
                i++;
        }
        return;
    }
}