[clang] [Clang] Add warning message for C++17 alias template CTAD (PR #133806)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

Perfect, thanks!  Whoever notices that CI is happy can merge this.  Remind us if you notice/cannot.

https://github.com/llvm/llvm-project/pull/133806