busybox: fix a compile error on mac os x

SVN-Revision: 28578

package/busybox/patches/920-portability.patch

+--- a/scripts/kconfig/mconf.c
++++ b/scripts/kconfig/mconf.c
+@@ -25,6 +25,10 @@
+ #include <unistd.h>
+ #include <locale.h>
+ 
++#ifndef SIGWINCH
++#define SIGWINCH 28
++#endif
++
+ #define LKC_DIRECT_LINK
+ #include "lkc.h"
+