TLS: Fix build on older verisons of OpenSSL.

src/tls.c

@@ -168,7 +168,9 @@ int tlsConfigure(redisTLSContextConfig *ctx_config) {
 
     SSL_CTX_set_mode(ctx, SSL_MODE_ENABLE_PARTIAL_WRITE|SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);
     SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_FAIL_IF_NO_PEER_CERT, NULL);
+#if defined(SSL_CTX_set_ecdh_auto)
     SSL_CTX_set_ecdh_auto(ctx, 1);
+#endif
 
     if (SSL_CTX_use_certificate_file(ctx, ctx_config->cert_file, SSL_FILETYPE_PEM) <= 0) {
         ERR_error_string_n(ERR_get_error(), errbuf, sizeof(errbuf));