Add release note

Author: henrybw

clang/docs/ReleaseNotes.rst

@@ -491,6 +491,8 @@ Bug Fixes in This Version
 - Accept empty enumerations in MSVC-compatible C mode. (#GH114402)
 - Fix a bug leading to incorrect code generation with complex number compound assignment and bitfield values, which also caused a crash with UBsan. (#GH166798)
 - Fixed false-positive shadow diagnostics for lambdas in explicit object member functions. (#GH163731)
+- Fix an assertion failure when a ``target_clones`` attribute is only on the
+  forward declaration of a multiversioned function. (#GH165517) (#GH129483)
 
 Bug Fixes to Compiler Builtins
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