kconfig: add missing <ctype.h> inclusion

This header is needed when using isspace(3) function family.
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>

scripts/kconfig/menu.c

@@ -3,6 +3,7 @@
  * Released under the terms of the GNU GPL v2.0.
  */
 
+#include <ctype.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>