Include wchar.h to improve our chances of finding

WCHAR_MAX.  This might fix a portability problem on HP_UX.

Thanks to: Susan Kim

lib/libarchive/archive_read_support_format_tar.c

@@ -33,6 +33,7 @@ __FBSDID("$FreeBSD$");
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <wchar.h>
 
 #include "archive.h"
 #include "archive_entry.h"