openssl: Explicitly include openssl/bn.h

If OpenSSL is compiled with OPENSSL_NO_DEPRECATED some of the headers
we include don't include openssl/bn.h anymore.  Therefore, we have to
explicitly include it ourselves where we use BN_* functions.

Fixes #1113.

src/libstrongswan/plugins/openssl/openssl_diffie_hellman.c

@@ -18,6 +18,7 @@
 
 #ifndef OPENSSL_NO_DH
 
+#include <openssl/bn.h>
 #include <openssl/dh.h>
 
 #include "openssl_diffie_hellman.h"

src/libstrongswan/plugins/openssl/openssl_ec_diffie_hellman.c

@@ -17,6 +17,7 @@
 
 #ifndef OPENSSL_NO_EC
 
+#include <openssl/bn.h>
 #include <openssl/ec.h>
 #include <openssl/objects.h>
 #include <openssl/bn.h>

src/libstrongswan/plugins/openssl/openssl_rsa_private_key.c

@@ -23,6 +23,7 @@
 
 #include <utils/debug.h>
 
+#include <openssl/bn.h>
 #include <openssl/evp.h>
 #include <openssl/rsa.h>
 #ifndef OPENSSL_NO_ENGINE

src/libstrongswan/plugins/openssl/openssl_rsa_public_key.c

@@ -23,6 +23,7 @@
 
 #include <utils/debug.h>
 
+#include <openssl/bn.h>
 #include <openssl/evp.h>
 #include <openssl/rsa.h>
 #include <openssl/x509.h>

src/libstrongswan/plugins/openssl/openssl_util.c

@@ -18,6 +18,7 @@
 
 #include <utils/debug.h>
 
+#include <openssl/bn.h>
 #include <openssl/evp.h>
 #include <openssl/x509.h>