Clarify the error message for malformed extern crate statements

Closes #25468.

src/test/parse-fail/extern-crate-unexpected-token.rs

@@ -0,0 +1,11 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+extern crte foo; //~ ERROR expected one of `crate`, `fn`, or `{`, found `crte`

src/test/parse-fail/extern-expected-fn-or-brace.rs

@@ -13,4 +13,4 @@
 // Verifies that the expected token errors for `extern crate` are
 // raised
 
-extern "C" mod foo; //~ERROR expected `{` or `fn`, found `mod`
+extern "C" mod foo; //~ERROR expected one of `fn` or `{`, found `mod`