In 87057e support for net-dns/libidn2 was added (see URL). This should be supported by the -9999/>233 ebuild.
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=8dbafb543a184817f1ee41edff917bf87dedf65b commit 8dbafb543a184817f1ee41edff917bf87dedf65b Author: Mike Gilbert <floppym@gentoo.org> Date: Sat May 13 17:03:09 2017 -0400 sys-apps/systemd: add libidn2 support Bug: https://bugs.gentoo.org/618384 Package-Manager: Portage-2.3.5_p32, Repoman-2.3.2_p62 sys-apps/systemd/metadata.xml | 1 + sys-apps/systemd/systemd-9999.ebuild | 20 +++++++++++++++++--- 2 files changed, 18 insertions(+), 3 deletions(-)