Request #18115 has been accepted by diabonas [1]: Sources are gone, so this package fails to build. Note that upstream moved to Git (https://github.com/gnustep/libobjc2), so a rename and major rewrite would be required to make this package work again, which is not worth the effort according to the former maintainer: "I disown this package. Reason: it was created for darling-git, but darling-git no longer depends on gnustep-libobjc2-clang-svn."
[1] https://aur.archlinux.org/account/diabonas/
