https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86368
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- It might be reasonable for GCC to silently ignore attributes that use an unrecognized attribute-namespace. If somebody uses [[clang::foobar]] or [[acme::rocketboots]] they probably aren't expecting GCC to handle it. This could mean silently ignoring typos like [[ngu::unused]] but it's arguably easier to spot a typo like "ngu" than to spot "warn_unsued_result" or "alwasy_inlne".
