The GTK2 -> 3 migration guide suggests removing deprecated usages as the first step, using the following flags. Even if we don't move to GTK3, this could be a good cleanup.

make CFLAGS+="-DGTK_DISABLE_SINGLE_INCLUDES"
make CFLAGS+="-DGDK_DISABLE_DEPRECATED -DGTK_DISABLE_DEPRECATED"
make CFLAGS+="-DGSEAL_ENABLE"