net-vpn/tor-0.3.0.10 still makes use of old OpenSSL < 1.1 API, which isn't enabled in Gentoo builds. This patch fixes it: https://raw.githubusercontent.com/gnu-andrew/crypto/master/net-vpn/tor/files/tor-openssl-1.1.0.patch
This should go upstream to the tor developers. I don't want to add a patch that hasn't been vetted by them first.
Sadly it doesn't seem upstream will fix this any time soon: https://trac.torproject.org/projects/tor/ticket/19429#comment:4 :(
this is off the tree. open a new bug if any of the newer versions are affected