Stop using --enable-fatal-warnings on GCC 0.2.8 builds
The 0.2.8 builds with GCC are failing on buster and sid when built with --enable-fatal-warnings, because of GCC warnings that were added in GCC 7. We don't plan to backport fixes for those warnings, since the fixes are fairly big, and 0.2.8 is only supported for another two months.
Maybe Jenkins should just remove --enable-fatal-warnings for these builders?
(Note that the configure option in question was formerly known as --enable-gcc-warnings : it's possible that the jenkins builders are invoking it by that name instead.)