add test for spurious intra-doc link warning

Author: QuietMisdreavus

src/test/rustdoc/auxiliary/intra-links-external-traits.rs

@@ -0,0 +1,6 @@
+pub trait ThisTrait {
+    fn asdf(&self);
+
+    /// let's link to [`asdf`](ThisTrait::asdf)
+    fn qwop(&self);
+}

src/test/rustdoc/intra-links-external-traits.rs

@@ -0,0 +1,12 @@
+// aux-build:intra-links-external-traits.rs
+// ignore-cross-compile
+
+#![crate_name = "outer"]
+#![deny(intra_doc_link_resolution_failure)]
+
+// using a trait that has intra-doc links on it from another crate (whether re-exporting or just
+// implementing it) used to give spurious resolution failure warnings
+
+extern crate intra_links_external_traits;
+
+pub use intra_links_external_traits::ThisTrait;