Add sentence that clarifies that the wording has recently been implemented by gcc.

Author: Dani-Hub

xml/issue4398.xml

@@ -28,7 +28,10 @@ However, formatting an adaptor requires formatting of the underlying range, and
 the nonlocking_optimizations for all ranges.
 <p/>
 This problem does not occur for the `flat_set`, `flat_map` adaptors, which are also ranges, and 
-do not have a specialized formatter, and use range one.
+do not have a specialized formatter.
+<p/>
+The proposed wording has recently been implemented in 
+<a href="https://gcc.gnu.org/pipermail/libstdc++/2025-October/063758.html">gcc's libstdc++</a>.
 </p>
 </discussion>