This is my syslinux ebuild against may github master repo which has a few extra patches in order to work with gnu-efi-3.06 !Note! Current Gentoo syslinux builds against a bundled(very old) gnu-efi Just sharing what I got should anyone else need a fresh gnu-efi install.
Created attachment 503422 [details] syslinux-6.9999.ebuild
This looks obsolete. syslinux upstream development is stale since 2019. Your git is at older date. If needed, we should add patches to sys-boot/syslinux-6.04_pre3* syslinux-6.04_pre3-r1.ebuild uses sys-boot/gnu-efi only syslinux-6.04_pre1-r5.ebuild seems to use bundled gnu-efi Unfortunately only the old syslinux-6.04_pre1-r5.ebuild is stabilized.