Update compiler tests for 2018-12-28 nightly.

core/codegen/tests/ui-fail/catch.rs

@@ -41,3 +41,5 @@ fn f3(_request: &Request, other: bool) {
     //~^ ERROR invalid number of arguments
     //~^^ HELP optionally take an argument
 }
+
+fn main() { }

core/codegen/tests/ui-fail/from_form.rs

@@ -1,5 +1,7 @@
 #[macro_use] extern crate rocket;
 
+use rocket::http::RawStr;
+
 #[derive(FromForm)]
 enum Thing { }
 //~^ ERROR not supported
@@ -162,3 +164,5 @@ struct BadName3 {
     //~^ ERROR invalid form field name
     field: String,
 }
+
+fn main() { }