Add regression test for doc_auto_cfg feature handling with glob reexports

tests/rustdoc/glob-reexport-attribute-merge-doc-auto-cfg.rs

@@ -0,0 +1,29 @@
+// This test ensures that non-glob reexports don't get their attributes merge with
+// the reexported item whereas glob reexports do with the `doc_auto_cfg` feature.
+
+#![crate_name = "foo"]
+#![feature(doc_auto_cfg)]
+
+// @has 'foo/index.html'
+// There are two items.
+// @count - '//*[@class="item-table"]//div[@class="item-name"]' 2
+// Only one of them should have an attribute.
+// @count - '//*[@class="item-table"]//div[@class="item-name"]/*[@class="stab portability"]' 1
+
+mod a {
+    #[cfg(not(feature = "a"))]
+    pub struct Test1;
+}
+
+mod b {
+    #[cfg(not(feature = "a"))]
+    pub struct Test2;
+}
+
+// @has 'foo/struct.Test1.html'
+// @count - '//*[@id="main-content"]/*[@class="item-info"]' 1
+// @has - '//*[@id="main-content"]/*[@class="item-info"]' 'Available on non-crate feature a only.'
+pub use a::*;
+// @has 'foo/struct.Test2.html'
+// @count - '//*[@id="main-content"]/*[@class="item-info"]' 0
+pub use b::Test2;