https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118337
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I wonder if the incompatibility isn't just about the iso-c-binding.def (and maybe iso-fortran-env.def) changes inserting stuff in the middle rather than always just appending it to the end. The 42 to 63 change is 21, and there are 21 NAMED_UINTCST entries added into the middle of iso-c-binding.def (and one NAMED_FUNCTION added at the end). iso-fortran-env.def has 5 NAMED_INTCST and 4 NAMED_UINTCSTs added into the middle. I don't know if those could be moved to the end and whether it would then work fine or not. And whether this is just about the intrindic modules or not. Though, even if stuff is just added at the end, I wonder if GCC 15 compiled *.mod files that use somewhere the new iso-c-binding etc. entries won't cause crashes when compiled by GCC 14. So maybe bumping MOD_VERSION is really the only solution. Note, diffing those *.def files between GCC 11 and 14, there were no additions/removals there.
