sys-fs/udev-242 also needs systemd's fix from bug 685534 in order to build successfully with GCC 9 as it is exactly the same codebase. Specifically, it was enough for me to apply the following patch to make it compile: https://patch-diff.githubusercontent.com/raw/systemd/systemd/pull/12641.patch
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=bedd1302f0fdf5d892f9bf8be663e6b3bfa3cb0e commit bedd1302f0fdf5d892f9bf8be663e6b3bfa3cb0e Author: Mike Gilbert <floppym@gentoo.org> AuthorDate: 2019-07-30 14:44:29 +0000 Commit: Mike Gilbert <floppym@gentoo.org> CommitDate: 2019-07-30 14:45:04 +0000 sys-fs/udev: backport fixes for gcc 9 Closes: https://bugs.gentoo.org/690356 Package-Manager: Portage-2.3.69_p3, Repoman-2.3.16_p12 Signed-off-by: Mike Gilbert <floppym@gentoo.org> sys-fs/udev/files/242-gcc-9.patch | 163 ++++++++++++++++++++++++++++++++++++++ sys-fs/udev/udev-242.ebuild | 1 + 2 files changed, 164 insertions(+)