Add recvmsg (stub on redox)

src/header/sys_socket/mod.rs

@@ -167,6 +167,11 @@ pub unsafe extern "C" fn recvfrom(
     )
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn recvmsg(socket: c_int, msg: *mut msghdr, flags: c_int) -> ssize_t {
+    Sys::recvmsg(socket, msg, flags)
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn send(
     socket: c_int,