[Bug c++/124284] Accepts invalid malformed attribute syntax with mismatched brackets

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124284

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think GCC is correct here. Only matching `()` is required for unkown
attributes.