Add libressl compatibility
LibreSSL is a fork of OpenSSL with a lot of the OpenSSL cruft removed (this was certainly true at the time LibreSSL started; I don't know exactly what the current state is). It is generally compatible with "modern" (un-crufty) uses of OpenSSL, but there are minor API differences.
There was a Phab diff that discussed this and at least partly implemented compatibility in early 2019; it looks stalled.
FreeBSD carries a patch -- which in turn comes from a mix of Gentoo and OpenBSD -- for LibreSSL compatibility. All I can say is that qca builds and can print a usage message: because of the pervasive nature of SSL, doing useful end-user testing means rebuilding an entire system with LibreSSL rather than OpenSSL. I'll run the tests from git, at least, once I have those building as well.