fix rustdoc stack overflow on mutually recursive Deref

fix #85095

src/test/rustdoc/issue-85095.rs

@@ -0,0 +1,22 @@
+use std::ops::Deref;
+
+pub struct A;
+pub struct B;
+
+// @has issue_85095/struct.A.html '//code' 'impl Deref for A'
+impl Deref for A {
+    type Target = B;
+
+    fn deref(&self) -> &Self::Target {
+        panic!()
+    }
+}
+
+// @has issue_85095/struct.B.html '//code' 'impl Deref for B'
+impl Deref for B {
+    type Target = A;
+
+    fn deref(&self) -> &Self::Target {
+        panic!()
+    }
+}