Rollup merge of #45122 - jean-lourenco:master, r=nikomatsakis

Better compile error output when using arguments instead of types

Following @estebank sugestion on issue https://github.com/rust-lang/rust/issues/18945#issuecomment-331251436

src/libsyntax/parse/parser.rs

@@ -2960,6 +2960,7 @@ impl<'a> Parser<'a> {
                 {                                  //     Foo<Bar<Baz<Qux, ()>>>
                     err.help(
                         "use `::<...>` instead of `<...>` if you meant to specify type arguments");
+                    err.help("or use `(...)` if you meant to specify fn arguments");
                 }
                 err.emit();
             }