message: also support writing to stderr
diff: @@ -587,11 +587,11 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  let buf = args[1].read_ptr(&self.memory)?;
  let n = self.value_to_primval(args[2], usize)?.to_u64()?;
  trace!("Called write({:?}, {:?}, {:?})", fd, buf, n);
  - let result = if fd == 1 { // stdout
  + let result = if fd == 1 || fd == 2 { // stdout/stderr
  use std::io::{self, Write};
  let buf_cont = self.memory.read_bytes(buf, n)?;
  - let res = io::stdout().write(buf_cont);
  + let res = if fd == 1 { io::stdout().write(buf_cont) } else { io::stderr().write(buf_cont) };
  match res { Ok(n) => n as isize, Err(_) => -1 }
  } else {
  info!("Ignored output to FD {}", fd);
  