SSL_CTX_set_ecdh_auto() is not defined when OpenSSL 1.1.1 is compiled
with the no-deprecated option. Remove existing, incomplete guards and
add a compatibility macro in openssl-compat.h, just as OpenSSL does:
bf4006a6f9/include/openssl/ssl.h (L1486)
This should be backported as far as 2.0 and probably even 1.9.