Place compile-fail expected errors on their own line

test_suite/tests/compile-fail/identifier/variant_tuple.rs

@@ -9,11 +9,12 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Deserialize)] //~ ERROR: 12:10: 12:21: variant_identifier may only contain unit variants
+#[derive(Deserialize)]
 #[serde(variant_identifier)]
 enum F {
     A,
     B(u8, u8),
+    //~^^^^^ ERROR: variant_identifier may only contain unit variants
 }
 
 fn main() {}