Function build_options

fn build_options<O: Default>(
    early_dcx: &EarlyDiagCtxt,
    matches: &Matches,
    descrs: &'static [(&'static str, fn(_: &mut O, v: Option<&str>) -> bool, &'static str, &'static str)],
    prefix: &str,
    outputname: &str,
) -> O