Properly detect endianness.

Index: cutils.h
--- cutils.h.orig
+++ cutils.h
@@ -28,8 +28,11 @@
 #include <stdlib.h>
 #include <inttypes.h>
 
-/* set if CPU is big endian */
-#undef WORDS_BIGENDIAN
+#include <endian.h>
+
+#if BYTE_ORDER == BIG_ENDIAN
+#define WORDS_BIGENDIAN
+#endif
 
 #define likely(x)       __builtin_expect(!!(x), 1)
 #define unlikely(x)     __builtin_expect(!!(x), 0)