tools: ifwitool: Define __packed when it is not defined

Some compilers may provide __packed define for us.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

tools/ifwitool.c

@@ -10,7 +10,9 @@
 #include <getopt.h>
 #include "os_support.h"
 
+#ifndef __packed
 #define __packed		__attribute__((packed))
+#endif
 #define KiB			1024
 #define ALIGN(x, a)		__ALIGN_MASK((x), (typeof(x))(a) - 1)
 #define __ALIGN_MASK(x, mask)	(((x) + (mask)) & ~(mask))