make c and cpp recipes depend on each other

[repelliuss]

When c-ts-mode.el loaded, it evaluates

(and (treesit-ready-p 'cpp)
     (treesit-ready-p 'c))

which pops up a warning every time even though treesit-auto install mode specific tree-sitter. This was unexpected as we asked treesit-auto to install libraries and it is okay with it. Users may still get the warning but before libraries are installed and only once across Emacs sessions.

This should fix #92 #104 #124 .