Warn on exhaustive exported enums

Enable clippy::exhaustive_enums in every crate so new exported enums
are either #[non_exhaustive] or explicitly allowed as a closed set.

winit-orbital/src/event_loop.rs

@@ -1,3 +1,5 @@
+// `EventSource` is macro-generated; the lint can't be allowed on the enum itself.
+#![allow(clippy::exhaustive_enums)]
 use std::cell::Cell;
 use std::collections::VecDeque;
 use std::sync::atomic::{AtomicBool, Ordering};

winit-orbital/src/lib.rs

@@ -3,6 +3,8 @@
 //! Redox OS has some functionality not yet present that will be implemented
 //! when its orbital display server provides it.
 
+#![warn(clippy::exhaustive_enums)]
+
 use std::fs::{File, OpenOptions};
 use std::io::{Read, Result, Write};
 use std::os::fd::AsRawFd;