Add/extend tests for deriving Clone

src/test/run-pass/deriving-clone-enum.rs

@@ -18,5 +18,10 @@ enum E {
 }
 
 pub fn main() {
-    let _ = E::A.clone();
+    let mut foo = E::A.clone();
+
+    // Test both code-paths of clone_from (same variant/different variant)
+    foo.clone_from(&E::A);
+    foo.clone_from(&E::B(()));
+    foo.clone_from(&E::B(()));
 }

src/test/run-pass/deriving-clone-generic-enum.rs

@@ -18,5 +18,10 @@ enum E<T,U> {
 }
 
 pub fn main() {
-    let _ = E::A::<isize, isize>(1).clone();
+    let mut foo = E::A::<isize, isize>(1).clone();
+
+    // Test both code-paths of clone_from (same variant/different variant)
+    foo.clone_from(&E::A(32));
+    foo.clone_from(&E::B(1, 2));
+    foo.clone_from(&E::B(3, 4));
 }

src/test/run-pass/deriving-clone-generic-struct.rs

@@ -18,5 +18,6 @@ struct S<T> {
 }
 
 pub fn main() {
-    let _ = S { foo: (), bar: (), baz: 1 }.clone();
+    let mut foo = S { foo: (), bar: (), baz: 1 }.clone();
+    foo.clone_from(&S { foo: (), bar: (), baz: 31 });
 }

src/test/run-pass/deriving-clone-generic-tuple-struct.rs

@@ -14,5 +14,6 @@
 struct S<T>(T, ());
 
 pub fn main() {
-    let _ = S(1, ()).clone();
+    let mut foo = S(1, ()).clone();
+    foo.clone_from(&S(32, ()));
 }