[Bug c++/84905] Improve warning for __attribute__((const)) on function returning void

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84905

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No suggestions here, I was just passing on it on. My response on IRC was pretty
much what you said: you need to read the manual to know what the attribute
does, the warning is not the place to put that info.