Point compile-fail errors to the input item instead of the derive

Author: dtolnay

src/test/compile-fail-fulldeps/rustc-macro/append-impl.rs

@@ -23,8 +23,8 @@ trait Append {
 #[derive(PartialEq,
          Append,
          Eq)]
-//~^^ ERROR: the semantics of constant patterns is not yet settled
 struct A {
+//~^ ERROR: the semantics of constant patterns is not yet settled
     inner: u32,
 }
 

src/test/compile-fail-fulldeps/rustc-macro/expand-to-unstable-2.rs

@@ -17,8 +17,8 @@
 extern crate derive_unstable_2;
 
 #[derive(Unstable)]
-//~^ ERROR: reserved for internal compiler
 struct A;
+//~^ ERROR: reserved for internal compiler
 
 fn main() {
     foo();

src/test/compile-fail-fulldeps/rustc-macro/expand-to-unstable.rs

@@ -17,8 +17,8 @@
 extern crate derive_unstable;
 
 #[derive(Unstable)]
-//~^ ERROR: use of unstable library feature
 struct A;
+//~^ ERROR: use of unstable library feature
 
 fn main() {
     unsafe { foo(); }