message: Use correct return type for syscall(SYS_futex).
diff: @@ -61,7 +61,7 @@ pub fn futex<'tcx>(
  None => {
  let einval = this.eval_libc("EINVAL")?;
  this.set_last_error(einval)?;
  - this.write_scalar(Scalar::from_i32(-1), dest)?;
  + this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
  return Ok(());
  }
  };
  @@ -81,7 +81,7 @@ pub fn futex<'tcx>(
  this.block_thread(thread);
  this.futex_wait(addr, thread);
  // Succesfully waking up from FUTEX_WAIT always returns zero.
  - this.write_scalar(Scalar::from_i32(0), dest)?;
  + this.write_scalar(Scalar::from_machine_isize(0, this), dest)?;
  // Register a timeout callback if a timeout was specified.
  // This callback will override the return value when the timeout triggers.
  if let Some(timeout_time) = timeout_time {
  @@ -93,7 +93,7 @@ pub fn futex<'tcx>(
  this.futex_remove_waiter(addr, thread);
  let etimedout = this.eval_libc("ETIMEDOUT")?;
  this.set_last_error(etimedout)?;
  - this.write_scalar(Scalar::from_i32(-1), dest)?;
  + this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
  Ok(())
  }),
  );
  @@ -103,7 +103,7 @@ pub fn futex<'tcx>(
  // right away without sleeping: -1 and errno set to EAGAIN.
  let eagain = this.eval_libc("EAGAIN")?;
  this.set_last_error(eagain)?;
  - this.write_scalar(Scalar::from_i32(-1), dest)?;
  + this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
  }
  }
  // FUTEX_WAKE: (int *addr, int op = FUTEX_WAKE, int val)
  @@ -121,7 +121,7 @@ pub fn futex<'tcx>(
  break;
  }
  }
  - this.write_scalar(Scalar::from_i32(n), dest)?;
  + this.write_scalar(Scalar::from_machine_isize(n, this), dest)?;
  }
  op => throw_unsup_format!("miri does not support SYS_futex operation {}", op),
  }
  