https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67064
--- Comment #14 from Jason Merrill <jason at gcc dot gnu.org> --- (In reply to Ville Voutilainen from comment #13) > It is correct that currently none of the pedantic-flags diagnose the use of > this extension; perhaps that should be fixed while fixing this bug... '-Wpedantic' does not cause warning messages for use of the alternate keywords whose names begin and end with '__'. Pedantic warnings are also disabled in the expression that follows '__extension__'. However, only system header files should use these escape routes; application programs should avoid them.