Properly report transitive errors

src/test/ui/const-eval/conditional_array_execution.rs

@@ -19,5 +19,7 @@ const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
 fn main() {
     println!("{}", FOO);
     //~^ WARN this expression will panic at runtime
+    //~| WARN referenced constant
     //~| ERROR erroneous constant used
+    //~| E0080
 }