Write correct value to kernel when exiting thread.

redox-rt/src/thread.rs

@@ -52,6 +52,6 @@ pub fn exit_this_thread() -> ! {
     let thread_fd = RtTcb::current().thread_fd();
     // TODO: modify interface so it writes directly to the thread fd?
     let status_fd = syscall::dup(**thread_fd, b"status").unwrap();
-    syscall::write(status_fd, &0_usize.to_ne_bytes()).unwrap();
+    syscall::write(status_fd, &usize::MAX.to_ne_bytes()).unwrap();
     unreachable!()
 }