Avoid getting unresolved referense to bn_expand2 in test/bntest.c

#include <openssl/x509.h>

#include <openssl/err.h>

/*

 * In bn_lcl.h, bn_expand() is defined as a static ossl_inline function.

 * This is fine in itself, it will end up as an unused static function in

 * the worst case.  However, it referenses bn_expand2(), which is a private

 * function in libcrypto and therefore unavailable on some systems.  This

 * may result in a linker error because of unresolved symbols.

 *

 * To avoid this, we define a dummy variant of bn_expand2() here, and to

 * avoid possible clashes with libcrypto, we rename it first, using a macro.

 */

#define bn_expand2 dummy_bn_expand2

static BIGNUM *bn_expand2(BIGNUM *b, int words) { return NULL; }

#include "../crypto/bn/bn_lcl.h"

static const int num0 = 100;           /* number of tests */