message: Return correct value from futex_wait.
diff: @@ -36,9 +36,11 @@ pub fn futex<'tcx>(
  if val == futex_val {
  this.block_thread(thread);
  this.futex_wait(futex_ptr, thread);
  + this.write_scalar(Scalar::from_i32(0), dest)?;
  } else {
  let eagain = this.eval_libc("EAGAIN")?;
  this.set_last_error(eagain)?;
  + this.write_scalar(Scalar::from_i32(-1), dest)?;
  }
  }
  op if op == futex_wake => {
  