Add a comment and remove redundant definitions.
# endif /* !be16toh */
#elif defined(_WIN32)
-/* Windows is always little endian */
-#include <stdlib.h>
+/*
+ * Windows is always little-endian and has its own byte-swapping routines, so
+ * use these.
+ */
+
+# include <stdlib.h>
# define htobe16(x) _byteswap_ushort(x)
# define htole16(x) (x)
# define be64toh(x) _byteswap_uint64(x)
# define le64toh(x) (x)
-# define __BYTE_ORDER BYTE_ORDER
-# define __BIG_ENDIAN BIG_ENDIAN
-# define __LITTLE_ENDIAN LITTLE_ENDIAN
-# define __PDP_ENDIAN PDP_ENDIAN
-
#elif defined __APPLE__
/*