BUILD: ssl: simplify SSL_CTX_set_ecdh_auto compatibility

SSL_CTX_set_ecdh_auto is declared (when present) with #define. A simple #ifdef
avoid to list all cases of ssllibs. It's a placebo in new ssllibs. It's ok with
openssl 1.0.1, 1.0.2, 1.1.0, libressl and boringssl.
Thanks to Piotr Kubaj for postponing and testing with libressl.
2 files changed