- Functions requiring File System functions can now be disables by undefining POLARSSL_FS_IO

diff --git a/library/bignum.c b/library/bignum.c
index a2b132d..8f29324 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -407,6 +407,7 @@
     return( ret );
 }
 
+#if defined(POLARSSL_FS_IO)
 /*
  * Read X from an opened file
  */
@@ -468,6 +469,7 @@
 
     return( ret );
 }
+#endif /* POLARSSL_FS_IO */
 
 /*
  * Import X from unsigned binary data, big endian