Expand ECN support

libc's CMSG macros got built out to many more platforms. There may
remain some obscure platforms where this will still fail to build, but
we can account for them as they show up in practice.

Author: Ralith

quinn/Cargo.toml

@@ -35,7 +35,7 @@ untrusted = "0.6.2"
 webpki = "0.19"
 webpki-roots = "0.16"
 ct-logs = "0.5"
-libc = "0.2.46"
+libc = "0.2.48"
 mio = "0.6"
 
 [dev-dependencies]

quinn/src/platform/mod.rs

@@ -2,15 +2,13 @@
 use quinn_proto::EcnCodepoint;
 use std::{io, net::SocketAddr};
 
-// The Linux code should work for most unixes, but as of this writing nobody's ported the
-// CMSG_... macros to the libc crate for any of the BSDs.
-#[cfg(target_os = "linux")]
+#[cfg(unix)]
 mod cmsg;
-#[cfg(target_os = "linux")]
-mod linux;
+#[cfg(unix)]
+mod unix;
 
 // No ECN support
-#[cfg(not(target_os = "linux"))]
+#[cfg(not(unix))]
 mod fallback;
 
 pub trait UdpExt {