Add Release note.

Author: shafik

clang/docs/ReleaseNotes.rst

@@ -477,6 +477,7 @@ Bug Fixes to C++ Support
 - Fix for clang incorrectly rejecting the default construction of a union with
   nontrivial member when another member has an initializer. (#GH81774)
 - Diagnose unresolved overload sets in non-dependent compound requirements. (#GH51246) (#GH97753)
+- Fix bug where we were diagnosing all constexpr member functions if the class had a virtual bases. (#GH97266)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^