https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85678
--- Comment #12 from Wilco <wilco at gcc dot gnu.org> --- (In reply to David Brown from comment #11) > Changing the default to "-fno-common" (and ideally > "-Werror=strict-prototypes -Werror=old-style-declaration > -Werror=missing-parameter-type") would have a lot smaller impact than > changing the default standard. Giving errors on old-style code by default sounds like a good idea. We could add -std=legacy similar to Fortran to support building old K&R code (and that would enable -fcommon by default).
