Use #[derive] for Copy/Clone in s! and friends.

Allows use of `#[cfg]` to skip items in an `s!` block without creating
invalid, orphaned `impl` blocks.

(backport <rust-lang#4038>)
(cherry picked from commit 44c548d)

src/macros.rs

@@ -82,16 +82,11 @@ macro_rules! s {
         __item! {
             #[repr(C)]
             #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
+            #[derive(Copy, Clone)]
             #[allow(deprecated)]
             $(#[$attr])*
             pub struct $i { $($field)* }
         }
-        #[allow(deprecated)]
-        impl ::Copy for $i {}
-        #[allow(deprecated)]
-        impl ::Clone for $i {
-            fn clone(&self) -> $i { *self }
-        }
     );
 }
 
@@ -106,13 +101,10 @@ macro_rules! s_paren {
     )* ) => ($(
         __item! {
             #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
+            #[derive(Copy, Clone)]
             $(#[$attr])*
             pub struct $i ( $($field)* );
         }
-        impl ::Copy for $i {}
-        impl ::Clone for $i {
-            fn clone(&self) -> $i { *self }
-        }
     )*);
 }
 
@@ -130,28 +122,19 @@ macro_rules! s_no_extra_traits {
     (it: $(#[$attr:meta])* pub union $i:ident { $($field:tt)* }) => (
         __item! {
             #[repr(C)]
+            #[derive(Copy, Clone)]
             $(#[$attr])*
             pub union $i { $($field)* }
         }
-
-        impl ::Copy for $i {}
-        impl ::Clone for $i {
-            fn clone(&self) -> $i { *self }
-        }
     );
 
     (it: $(#[$attr:meta])* pub struct $i:ident { $($field:tt)* }) => (
         __item! {
             #[repr(C)]
+            #[derive(Copy, Clone)]
             $(#[$attr])*
             pub struct $i { $($field)* }
         }
-        #[allow(deprecated)]
-        impl ::Copy for $i {}
-        #[allow(deprecated)]
-        impl ::Clone for $i {
-            fn clone(&self) -> $i { *self }
-        }
     );
 }
 
@@ -177,13 +160,10 @@ macro_rules! e {
     )*) => ($(
         __item! {
             #[cfg_attr(feature = "extra_traits", derive(Debug, Eq, Hash, PartialEq))]
+            #[derive(Copy, Clone)]
             $(#[$attr])*
             pub enum $i { $($field)* }
         }
-        impl ::Copy for $i {}
-        impl ::Clone for $i {
-            fn clone(&self) -> $i { *self }
-        }
     )*);
 }