Add test to ensure foreign functions from dependencies are correctly handled

Author: GuillaumeGomez

src/test/rustdoc/reexport-dep-foreign-fn.rs

@@ -0,0 +1,12 @@
+// aux-build:all-item-types.rs
+
+// This test is to ensure there is no problem on handling foreign functions
+// coming from a dependency.
+
+#![crate_name = "foo"]
+
+extern crate all_item_types;
+
+// @has 'foo/fn.foo_ffn.html'
+// @has - '//*[@class="docblock item-decl"]//code' 'pub unsafe extern "C" fn foo_ffn()'
+pub use all_item_types::foo_ffn;