Add regression test

Author: inquisitivecrystal

src/test/rustdoc/macro-private-not-documented.rs

@@ -0,0 +1,19 @@
+// Checks that private macros aren't documented by default. They
+// should be still be documented in `--document-private-items` mode,
+// but that's tested in `macro-document-private.rs`.
+//
+//
+// This is a regression text for issue #88453.
+#![feature(decl_macro)]
+
+// @!has macro_private_not_documented/index.html 'a_macro'
+// @!has macro_private_not_documented/macro.a_macro.html
+macro_rules! a_macro {
+    () => ()
+}
+
+// @!has macro_private_not_documented/index.html 'another_macro'
+// @!has macro_private_not_documented/macro.another_macro.html
+macro another_macro {
+    () => ()
+}