SSL: fix build with OPENSSL_NO_ENGINE and/or OPENSSL_NO_OCSP.

This is really just a prerequisite for building against BoringSSL,
which doesn't provide either of those features.

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 d037f13..91c752c 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -3279,6 +3279,8 @@
 static char *
 ngx_openssl_engine(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 {
+#ifndef OPENSSL_NO_ENGINE
+
     ngx_openssl_conf_t *oscf = conf;
 
     ENGINE     *engine;
@@ -3313,6 +3315,12 @@
     ENGINE_free(engine);
 
     return NGX_CONF_OK;
+
+#else
+
+    return "is not supported";
+
+#endif
 }
 
 
@@ -3320,5 +3328,7 @@
 ngx_openssl_exit(ngx_cycle_t *cycle)
 {
     EVP_cleanup();
+#ifndef OPENSSL_NO_ENGINE
     ENGINE_cleanup();
+#endif
 }

src/event/ngx_event_openssl.h

diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index 174c865..4086940 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -18,9 +18,13 @@
 #include <openssl/conf.h>
 #include <openssl/crypto.h>
 #include <openssl/dh.h>
+#ifndef OPENSSL_NO_ENGINE
 #include <openssl/engine.h>
+#endif
 #include <openssl/evp.h>
+#ifndef OPENSSL_NO_OCSP
 #include <openssl/ocsp.h>
+#endif
 #include <openssl/rand.h>
 #include <openssl/rsa.h>
 #include <openssl/x509.h>

src/event/ngx_event_openssl_stapling.c

diff --git a/src/event/ngx_event_openssl_stapling.c b/src/event/ngx_event_openssl_stapling.c
index 69340b3..2fa0673 100644
--- a/src/event/ngx_event_openssl_stapling.c
+++ b/src/event/ngx_event_openssl_stapling.c
@@ -11,7 +11,7 @@
 #include <ngx_event_connect.h>
 
 
-#ifdef SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB
+#if (!defined OPENSSL_NO_OCSP && defined SSL_CTRL_SET_TLSEXT_STATUS_REQ_CB)
 
 
 typedef struct {