message: set errno on stdout write failure
diff: @@ -133,8 +133,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  };
  match res {
  Ok(n) => i64::try_from(n).unwrap(),
  - // FIXME: set errno to appropriate value
  - Err(_) => -1,
  + Err(e) => {
  + this.set_last_error_from_io_error(e)?;
  + -1
  + }
  }
  } else {
  this.write(fd, buf, count)?
  