Fix [-Werror=implicit-function-declaration] compiler error

The fileno() is only available if its feature test macro passes.  The
various symbols are defined appropriately in ../include/sane/config.h
during configuration of the build.

frontend/sicc.c

@@ -15,6 +15,8 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
 
+#include "../include/sane/config.h"
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/stat.h>