https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60512
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> --- N.B. checking #if __cpp_attributes works correctly with all versions of GCC (with a true result since 4.9.2 and false otherwise), whereas adding a new __has_feature extension and using #if __has_feature(attributes) would only give the right answer for GCC releases that support the feature.
