[clang] [clang] Add diagnostic for friend declaration of closure type member (PR #191419)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Also make sure to run tests, because changes you made in `cwg17xx.cpp` would not pass tests. If you're using `make` or `ninja`, C++ DR tests can be run with `ninja check-clang-cxx-drs`.

https://github.com/llvm/llvm-project/pull/191419