=app-misc/ca-certificates-20150426.3.20-r1 depends on >=app-misc/c_rehash-1.7-r1 which in turn requires >=dev-libs/openssl-1.0.2d-r2 The ebuild file from gentoo-x86 portage works just fine https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-libs/openssl/openssl-1.0.2d-r2.ebuild
There's a catch, the c_rehash script need to be patched to look into $EPREFIX instead of /. I'm away from my MBP, will post the patch later. (should be obvious if you want to patch that up yourself)
hmmm, the ebuild for c_rehash appears to fix it for prefix already...