message: unistd: use .is_null() for pointers
diff: @@ -30,12 +30,12 @@ pub unsafe extern "C" fn getopt(
  argv: *const *mut c_char,
  optstring: *const c_char,
  ) -> c_int {
  - if CURRENT_OPT == ptr::null_mut() || *CURRENT_OPT == 0 {
  + if CURRENT_OPT.is_null() || *CURRENT_OPT == 0 {
  if optind >= argc {
  -1
  } else {
  let current_arg = *argv.offset(optind as isize);
  - if current_arg == ptr::null_mut() || *current_arg != b'-' as c_char
  + if current_arg.is_null() || *current_arg != b'-' as c_char
  || string::strcmp(current_arg, b"-\0".as_ptr() as _) == 0
  {
  -1
  