[Bug c++/68230] Unused function parameters not reported by -Wunused-parameter when only used recursively.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68230

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Those aren't portable, so aren't a good general solution.