I built my kernel from genkernel. kernel is gentoo-sources. i enabled systemd per documentation. CONFIG_SYSFS_DEPRECATED and CONFIG_SYSFS_DEPRECATED_V2 were eanbled in the kernel and caused disk mount issues. after much digging, i disabled these and kernel builds fine. systemd ebuild should warn if these exist in the kernel. genkernel should disable these by default.
systemd-238-r3.ebuild: pkg_pretend() { if [[ ${MERGE_TYPE} != buildonly ]]; then local CONFIG_CHECK="~AUTOFS4_FS ~BLK_DEV_BSG ~CGROUPS ~CHECKPOINT_RESTORE ~DEVTMPFS ~EPOLL ~FANOTIFY ~FHANDLE ~INOTIFY_USER ~IPV6 ~NET ~NET_NS ~PROC_FS ~SIGNALFD ~SYSFS ~TIMERFD ~TMPFS_XATTR ~UNIX ~CRYPTO_HMAC ~CRYPTO_SHA256 ~CRYPTO_USER_API_HASH ~!FW_LOADER_USER_HELPER_FALLBACK ~!GRKERNSEC_PROC ~!IDE ~!SYSFS_DEPRECATED ~!SYSFS_DEPRECATED_V2" Looks like it's already in place.