SSL: fixed SSL_clear_options() usage with OpenSSL 1.1.0+.

In OpenSSL 1.1.0 the SSL_CTRL_CLEAR_OPTIONS macro was removed, so
conditional compilation test on it results in SSL_clear_options()
and SSL_CTX_clear_options() not being used.  Notably, this caused
"ssl_prefer_server_ciphers off" to not work in SNI-based virtual
servers if server preference was switched on in the default server.

It looks like the only possible fix is to test OPENSSL_VERSION_NUMBER
explicitly.

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 1b20745..df4fe0b 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -296,7 +296,7 @@
 
     SSL_CTX_set_options(ssl->ctx, SSL_OP_SINGLE_DH_USE);
 
-#ifdef SSL_CTRL_CLEAR_OPTIONS
+#if OPENSSL_VERSION_NUMBER >= 0x009080dfL
     /* only in 0.9.8m+ */
     SSL_CTX_clear_options(ssl->ctx,
                           SSL_OP_NO_SSLv2|SSL_OP_NO_SSLv3|SSL_OP_NO_TLSv1);

src/http/ngx_http_request.c

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 2db7a62..c88c271 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -923,7 +923,7 @@
 
         SSL_set_verify_depth(ssl_conn, SSL_CTX_get_verify_depth(sscf->ssl.ctx));
 
-#ifdef SSL_CTRL_CLEAR_OPTIONS
+#if OPENSSL_VERSION_NUMBER >= 0x009080dfL
         /* only in 0.9.8m+ */
         SSL_clear_options(ssl_conn, SSL_get_options(ssl_conn) &
                                     ~SSL_CTX_get_options(sscf->ssl.ctx));