bug#64917: 30.0.50; c-ts-mode throws warnings about missing cpp support

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: eliz@gnu.org, 64917@debbugs.gnu.org
> Date: Sun, 30 Jul 2023 21:43:18 -0400
> 
>       > Eli> Please install the C++ grammar as well.  Those two go together 
> because
>       > Eli> some *.h files could be C or C++, and we can only test that at 
> run
>       > Eli> time.
> 
> I suggest we ought to make a way for a user who never operates on C++
> programs to deactivate C++, deactivate this test, and not load
> anything for C++.

If someone finds a way of doing that without any significant
downsides, I won't object.  It's just that we haven't found such a way
yet.

Btw, the Emacs tree already includes a few files in C++, so having
this grammar available is necessary for work on Emacs.