[clang] [Clang] Add diagnostic for why std::is_abstract is false (PR #156199)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

1 comment, otherwise the comments that @shafik made are all valid/need to be dealt with, I'm happy when he is.

https://github.com/llvm/llvm-project/pull/156199