rustc: Encode the visibility of foreign items

Closes #16725

src/librustc/metadata/encoder.rs

@@ -1371,6 +1371,7 @@ fn encode_info_for_foreign_item(ecx: &EncodeContext,
 
     rbml_w.start_tag(tag_items_data_item);
     encode_def_id(rbml_w, local_def(nitem.id));
+    encode_visibility(rbml_w, nitem.vis);
     match nitem.node {
       ForeignItemFn(..) => {
         encode_family(rbml_w, style_fn_family(NormalFn));

src/test/auxiliary/issue-16725.rs

@@ -0,0 +1,14 @@
+// Copyright 2014 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 {
+    fn bar();
+}
+

src/test/compile-fail/issue-16725.rs

@@ -0,0 +1,19 @@
+// Copyright 2014 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.
+
+// aux-build:issue-16725.rs
+
+extern crate foo = "issue-16725";
+
+fn main() {
+    unsafe { foo::bar(); }
+    //~^ ERROR: function `bar` is private
+}
+