[Bug c++/87407] Enhance -Wunused-function to handle also inline functions

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87407

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Test the warning out on clang from a header file and you will see you get the
warning in the header too.  As I said I actually ran into this while working on
the vpp project and cursed clang for having this warning turned on.