sys-devel/clang was kept for a reason. Now sys-devel/llvm[clang] flag is going away, so fix your dependencies.
Fixed, and revbumped: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=e4e1e3265b573cead45703c35440179a8dc703fd https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=e7f94f58997f9d3e11a7e09684d4f1aa17df395a