Add test

src/test/rustdoc/intra-link-extern-type.rs

@@ -0,0 +1,18 @@
+#![feature(extern_types)]
+
+extern {
+    pub type ExternType;
+}
+
+impl ExternType {
+    pub fn f(&self) {
+
+    }
+}
+
+// @has 'intra_link_extern_type/foreigntype.ExternType.html'
+// @has 'intra_link_extern_type/fn.links_to_extern_type.html' \
+// 'href="../intra_link_extern_type/foreigntype.ExternType.html#method.f"'
+/// See also [ExternType::f]
+pub fn links_to_extern_type() {
+}