SSL: guard use of SSL_OP_MSIE_SSLV2_RSA_PADDING.

This option had no effect since 0.9.7h / 0.9.8b and it was removed
in recent OpenSSL.

Signed-off-by: Piotr Sikora <piotr@cloudflare.com>

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index f2419e4..fedb604 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -185,8 +185,10 @@
     SSL_CTX_set_options(ssl->ctx, SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG);
     SSL_CTX_set_options(ssl->ctx, SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER);
 
+#ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
     /* this option allow a potential SSL 2.0 rollback (CAN-2005-2969) */
     SSL_CTX_set_options(ssl->ctx, SSL_OP_MSIE_SSLV2_RSA_PADDING);
+#endif
 
     SSL_CTX_set_options(ssl->ctx, SSL_OP_SSLEAY_080_CLIENT_DH_BUG);
     SSL_CTX_set_options(ssl->ctx, SSL_OP_TLS_D5_BUG);