Link new bn_mod_exp_zero test to build

Author: tb

src/regress/lib/libcrypto/bn/Makefile

@@ -1,10 +1,11 @@
-#	$OpenBSD: Makefile,v 1.14 2022/12/02 08:30:54 tb Exp $
+#	$OpenBSD: Makefile,v 1.15 2022/12/02 17:34:26 tb Exp $
 
 PROGS +=	bn_add_sub
 PROGS +=	bn_cmp
 PROGS +=	bn_isqrt
 PROGS +=	bn_mod_exp
 PROGS +=	bn_mod_exp2_mont
+PROGS +=	bn_mod_exp_zero
 PROGS +=	bn_mod_sqrt
 PROGS +=	bn_mont
 PROGS +=	bn_primes
@@ -14,6 +15,7 @@ PROGS +=	bn_unit
 
 STATIC_LINK +=	bn_isqrt
 STATIC_LINK +=	bn_mod_exp
+STATIC_LINK +=	bn_mod_exp_zero
 STATIC_LINK +=	bn_primes
 STATIC_LINK +=	bn_rand_interval
 STATIC_LINK +=	bn_to_string