Add release note

Author: camc

clang/docs/ReleaseNotes.rst

@@ -308,6 +308,8 @@ Bug Fixes in This Version
 - Builtin elementwise operators now accept vector arguments that have different
   qualifiers on their elements. For example, vector of 4 ``const float`` values
   and vector of 4 ``float`` values. (#GH155405)
+- Stop rejecting C++11-style attributes on the first argument of constructors in older
+  standards. (#GH156809).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^