[Bug c/103960] Clang's -Wunknown-attributes is more useful than -Wattributes

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103960

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So it looks like the warning is coming from the front-end though and not from
c-family :).

I noticed this because take:
struct MyStruct;
[[gg (read_only, 1)]] int my_func (const struct MyStruct * const self);

----- CUT ----
The C front-end produces:
<source>:2:1: warning: 'gg' attribute ignored [-Wattributes]

While the C++ front-end produces:
<source>:2:70: warning: 'gg' attribute directive ignored [-Wattributes]