[Bug c++/88344] sole attribute specification in a class silently accepted

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88344

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The same is true for C2x and C++11 style attributes:
struct B {
  [[gnu::always_inline]];
};

The C front-end warns:
<source>:3:3: warning: 'always_inline' attribute ignored [-Wattributes]
    3 |   [[gnu::always_inline]];
      |   ^