It compiles without problem with libressl. The ebuild just need to add the choice between both implementation as shown in https://wiki.gentoo.org/wiki/Project:LibreSSL
Thanks for notifying me. I’ve done some further testing, actually running it a bit with LibreSSL in a chroot and it works fine AFAICT. Pull request submitted <https://github.com/gentoo/gentoo/pull/4940>.
Fixed in 0.2.0-r4 added in 4fbd7aae1abf3bedaf8c1c2eb71e72ae5f83a057.