[clang] [C] Diagnose use of C++ keywords in C (PR #137234)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> > Maybe `-Wkeyword-in-c++` or `-Wc++-keyword` would be a more concise name for the group?
> 
> I'm not tied to the name I picked, so either of these is fine by me. GCC doesn't split this into its own warning group, so we've got some latitude.
> 
> Any strong preferences?

FWIW I feel like the current one feels quite artificial. I think `-Wc++-keyword` is kinda nice, since it feels very similar to `-Wc++-compat`, but I don't have strong preferences.


https://github.com/llvm/llvm-project/pull/137234