message: test subtracting SystemTime and Instant
diff: @@ -9,10 +9,22 @@ fn main() {
  for _ in 0..10 { drop(vec![42]); }
  let now2 = SystemTime::now();
  assert!(now2 > now1);
  + let diff = now2.duration_since(now1).unwrap();
  + assert!(diff.as_micros() > 0);
  + assert_eq!(now1 + diff, now2);
  + assert_eq!(now2 - diff, now1);
  let now1 = Instant::now();
  // Do some work to make time pass.
  for _ in 0..10 { drop(vec![42]); }
  let now2 = Instant::now();
  assert!(now2 > now1);
  +
  + #[cfg(target_os = "linux")]
  + {
  + let diff = now2.duration_since(now1);
  + assert!(diff.as_micros() > 0);
  + assert_eq!(now1 + diff, now2);
  + assert_eq!(now2 - diff, now1);
  + }
  }
  