Fix builds when config.h only defines MBEDTLS_BIGNUM_C

Fixes #4929

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/programs/fuzz/common.c b/programs/fuzz/common.c
index ac39ee2..e12ee3b 100644
--- a/programs/fuzz/common.c
+++ b/programs/fuzz/common.c
@@ -1,4 +1,5 @@
 #include "common.h"
+#include <limits.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>