Add test for re-exports

I had a hard time getting this to work without the `extern crate`,
suggestions are welcome.

Author: jyn514

src/test/rustdoc/intra-doc-crate/auxiliary/submodule.rs

@@ -0,0 +1,12 @@
+#![crate_name = "bar"]
+
+pub trait Foo {
+    /// [`Bar`] [`Baz`]
+    fn foo();
+}
+
+pub trait Bar {
+}
+
+pub trait Baz {
+}

src/test/rustdoc/intra-doc-crate/basic.rs

@@ -1,5 +1,7 @@
 // aux-build:intra-doc-basic.rs
 // build-aux-docs
+
+// from https://github.com/rust-lang/rust/issues/65983
 extern crate a;
 
 // @has 'basic/struct.Bar.html' '//a[@href="../a/struct.Foo.html"]' 'Foo'

src/test/rustdoc/intra-doc-crate/submodule.rs

@@ -0,0 +1,14 @@
+// aux-build:submodule.rs
+// edition:2018
+extern crate bar as bar_;
+
+// from https://github.com/rust-lang/rust/issues/60883
+pub mod bar {
+    pub use ::bar_::Bar;
+}
+
+// NOTE: we re-exported both `Foo` and `Bar` here,
+// NOTE: so they are inlined and therefore we link to the current module.
+// @has 'submodule/trait.Foo.html' '//a[@href="../submodule/bar/trait.Bar.html"]' 'Bar'
+// @has 'submodule/trait.Foo.html' '//a[@href="../submodule/trait.Baz.html"]' 'Baz'
+pub use ::bar_::{Foo, Baz};