Build with opaque LibreSSL
LibreSSL in OpenBSD-current now has opaque structures like recent OpenSSL.
There's a few quirks to this:
LibreSSL doesn't have the SSL_get_client_ciphers() function. It's currently assumed that if OPENSSL_OPAQUE is set that function will exist.
Fixing this (probably?) shouldn't use LIBRESSL_VERSION_NUMBER because that only changes when a new versions of libresl-portable is released, so the libressl in -current with opaque structures still has the same LIBRESSL_VERSION_NUMBER as the released version of LibreSSL without opaque structures.
The SSL_STATE_STR hasn't changed in LibreSSL like it apparently did in OpenSSL 1.1.0.