[Bug debug/66869] [6 regression] -Wunused-function no longer warns for static declarations without definition

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66869

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Another possibility would be for warn_unused_function to add even the seemingly
unused decls into the cgraph and let the cgraph code actually complain.