Place compile-fail expected errors on their own line

test_suite/tests/compile-fail/enum-representation/internal-tuple-variant.rs

@@ -9,8 +9,9 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: #[serde(tag = "...")] cannot be used with tuple variants
+#[derive(Serialize)]
 #[serde(tag = "type")]
+//~^^ ERROR: #[serde(tag = "...")] cannot be used with tuple variants
 enum E {
     Tuple(u8, u8),
 }

test_suite/tests/compile-fail/enum-representation/internally-tagged-struct.rs

@@ -9,8 +9,9 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: #[serde(tag = "...")] can only be used on enums
+#[derive(Serialize)]
 #[serde(tag = "type")]
+//~^^ ERROR: #[serde(tag = "...")] can only be used on enums
 struct S;
 
 fn main() {}

test_suite/tests/compile-fail/enum-representation/untagged-and-internal.rs

@@ -9,9 +9,10 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: enum cannot be both untagged and internally tagged
+#[derive(Serialize)]
 #[serde(untagged)]
 #[serde(tag = "type")]
+//~^^^ ERROR: enum cannot be both untagged and internally tagged
 enum E {
     A(u8),
     B(String),

test_suite/tests/compile-fail/enum-representation/untagged-struct.rs

@@ -9,8 +9,9 @@
 #[macro_use]
 extern crate serde_derive;
 
-#[derive(Serialize)] //~ ERROR: 12:10: 12:19: #[serde(untagged)] can only be used on enums
+#[derive(Serialize)]
 #[serde(untagged)]
+//~^^ ERROR: #[serde(untagged)] can only be used on enums
 struct S;
 
 fn main() {}