Rollup merge of #21602 - japaric:derive-copy, r=alexcrichton

src/test/run-make/extern-fn-with-packed-struct/test.rs

@@ -9,15 +9,13 @@
 // except according to those terms.
 
 #[repr(packed)]
-#[derive(PartialEq, Show)]
+#[derive(Copy, PartialEq, Show)]
 struct Foo {
     a: i8,
     b: i16,
     c: i8
 }
 
-impl Copy for Foo {}
-
 #[link(name = "test", kind = "static")]
 extern {
     fn foo(f: Foo) -> Foo;