[clang] [clang][Itanium Mangle] Enable mangling of enclosing class for member… (PR #110503)

[Haojian Wu via cfe-commits]

hokein wrote:

Thanks.

Can you update the comment [here](https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/LangOptions.h#L242-L245) to mention this case? 

And I think it is better to move the release note `Mangle friend function ...` from the `Bug Fixes to C++ Support` to `ABI Changes in This Version`.

https://github.com/llvm/llvm-project/pull/110503