Function mbsrtowcs 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn mbsrtowcs(
    dst: *mut wchar_t,
    src: *mut *const c_char,
    len: size_t,
    ps: *mut mbstate_t,
) -> size_t

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

Convert a multibyte string to a wide string.