bignum: Add missing include.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Aris Adamantiadis <aris@0xbadc0de.be>

src/bignum.c

@@ -19,6 +19,8 @@
  * MA 02111-1307, USA.
  */
 
+#include <stdio.h>
+
 #include "libssh/priv.h"
 #include "libssh/bignum.h"
 #include "libssh/string.h"