[Bug c/107947] __has_c_attribute incorrectly identifies attribute as supported

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107947

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
To expand on the invalid placement of the attribute, the C++ front-end also
rejects it and also see PR 101682 which is also asking about it, gnulib was
broken at one point.

I did find that clang accepts the invalid placement of the attribute for its C
front-end in non-pedantic mode which might be the reason why some folks think
it should work.