Place compile-fail expected errors on their own line

test_suite/tests/compile-fail/unknown-attribute/container.rs

@@ -9,8 +9,9 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: unknown serde container attribute `abc`
+#[derive(Serialize)]
 #[serde(abc="xyz")]
+//~^^ ERROR: unknown serde container attribute `abc`
 struct A {
     x: u32,
 }

test_suite/tests/compile-fail/unknown-attribute/field.rs

@@ -9,9 +9,10 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: unknown serde field attribute `abc`
+#[derive(Serialize)]
 struct C {
     #[serde(abc="xyz")]
+    //~^^^ ERROR: unknown serde field attribute `abc`
     x: u32,
 }
 

test_suite/tests/compile-fail/unknown-attribute/variant.rs

@@ -9,9 +9,10 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: unknown serde variant attribute `abc`
+#[derive(Serialize)]
 enum E {
     #[serde(abc="xyz")]
+    //~^^^ ERROR: unknown serde variant attribute `abc`
     V,
 }