Build the new bignum_new.c file

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index e96a797..97ad178 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -2009,7 +2009,7 @@
  *
  * Enable the multi-precision integer library.
  *
- * Module:  library/bignum.c
+ * Module:  library/bignum.c, library/bignum_new.c
  * Caller:  library/dhm.c
  *          library/ecp.c
  *          library/ecdsa.c