libc can't use derive(Copy,Clone) because it doesn't work in rustc

src/unix/linux_like/linux/gnu/mod.rs

@@ -317,7 +317,6 @@ cfg_if! {
     if #[cfg(libc_union)] {
         // Internal, for casts to access union fields
         #[repr(C)]
-        #[derive(Copy,Clone)]
         struct sifields_sigchld {
             si_pid: ::pid_t,
             si_uid: ::uid_t,
@@ -325,6 +324,12 @@ cfg_if! {
             si_utime: ::c_long,
             si_stime: ::c_long,
         }
+        impl ::Copy for sifields_sigchld {}
+        impl ::Clone for sifields_sigchld {
+            fn clone(&self) -> sifields_sigchld {
+                *self
+            }
+        }
 
         // Internal, for casts to access union fields
         #[repr(C)]