Function vswprintf 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn vswprintf(
    s: *mut wchar_t,
    n: size_t,
    format: *const wchar_t,
    arg: VaList<'_>,
) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/vfwprintf.html.