Adjust atomics in the lio_listio doc test

Since changing the compiler version, this test has begun to occasionally
hang in CI.  And it's not just in QEMU.  It's probably due to an atomic
ordering problem.

Author: asomers

src/sys/aio.rs

@@ -1154,12 +1154,12 @@ pub fn aio_suspend(
 /// pub static SIGNALED: AtomicBool = AtomicBool::new(false);
 ///
 /// extern fn sigfunc(_: c_int) {
-///     SIGNALED.store(true, Ordering::Relaxed);
+///     SIGNALED.store(true, Ordering::Release);
 /// }
 /// let sa = SigAction::new(SigHandler::Handler(sigfunc),
 ///                         SaFlags::SA_RESETHAND,
 ///                         SigSet::empty());
-/// SIGNALED.store(false, Ordering::Relaxed);
+/// SIGNALED.store(false, Ordering::Release);
 /// unsafe { sigaction(Signal::SIGUSR2, &sa) }.unwrap();
 ///
 /// const WBUF: &[u8] = b"abcdef123456";
@@ -1173,7 +1173,7 @@ pub fn aio_suspend(
 /// ));
 /// let sev = SigevNotify::SigevSignal { signal: Signal::SIGUSR2, si_value: 0 };
 /// lio_listio(LioMode::LIO_NOWAIT, &mut[aiow.as_mut()], sev).unwrap();
-/// while !SIGNALED.load(Ordering::Relaxed) {
+/// while !SIGNALED.load(Ordering::Acquire) {
 ///     thread::sleep(time::Duration::from_millis(10));
 /// }
 /// // At this point, since `lio_listio` returned success and delivered its