Add regression test for rust-lang#113982

Author: GuillaumeGomez

tests/rustdoc/auxiliary/issue-113982-doc_auto_cfg-reexport-foreign.rs

@@ -0,0 +1,3 @@
+#![crate_name = "colors"]
+
+pub struct Color;

tests/rustdoc/issue-113982-doc_auto_cfg-reexport-foreign.rs

@@ -0,0 +1,19 @@
+// aux-build: issue-113982-doc_auto_cfg-reexport-foreign.rs
+
+#![feature(no_core, doc_auto_cfg)]
+#![no_core]
+#![crate_name = "foo"]
+
+extern crate colors;
+
+// @has 'foo/index.html' '//*[@class="stab portability"]' 'Non-colors'
+// @has 'foo/struct.Color.html' '//*[@class="stab portability"]' \
+//      'Available on non-crate feature colors only.'
+#[cfg(not(feature = "colors"))]
+pub use colors::*;
+
+// @has 'foo/index.html' '//*[@class="stab portability"]' 'Non-fruits'
+// @has 'foo/struct.Red.html' '//*[@class="stab portability"]' \
+//      'Available on non-crate feature fruits only.'
+#[cfg(not(feature = "fruits"))]
+pub use colors::Color as Red;