[clang] [Clang][Sema] Reject invalid member using-declaration whose nested-name-specifier doesn't refer to a base class of the current class in C++98 mode (PR #143492)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

I think we need an entry in "Potentially breaking changes" section.
Also, you should shorten the title of the PR, so that commit message is not overly long. Maybe something along the lines of `[clang] Require member using-declarations to name a base class`.

https://github.com/llvm/llvm-project/pull/143492