Implement AsFd/AsRawFd for EventLoop<T>

This should help other crates to integrate winit's event loop into
their bigger event loop without adding an extra thread.

src/platform_impl/linux/mod.rs

@@ -3,6 +3,7 @@
 #[cfg(all(not(x11_platform), not(wayland_platform)))]
 compile_error!("Please select a feature to build for unix: `x11`, `wayland`");
 
+use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
 use std::sync::Arc;
 use std::time::Duration;
 use std::{collections::VecDeque, env, fmt};
@@ -827,6 +828,18 @@ impl<T: 'static> EventLoop<T> {
     }
 }
 
+impl<T> AsFd for EventLoop<T> {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.as_fd())
+    }
+}
+
+impl<T> AsRawFd for EventLoop<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.as_raw_fd())
+    }
+}
+
 impl<T: 'static> EventLoopProxy<T> {
     pub fn send_event(&self, event: T) -> Result<(), EventLoopClosed<T>> {
         x11_or_wayland!(match self; EventLoopProxy(proxy) => proxy.send_event(event))