busybox: fix a compile error on mac os x

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@28578 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/busybox/patches/920-portability.patch

@@ -0,0 +1,13 @@
+--- 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"
+