Make byteorder conv functions compile on OS X.

refs #1558

src/libknot/util/endian.h

@@ -26,6 +26,14 @@
 #	define be16toh(x) betoh16(x)
 #	define be32toh(x) betoh32(x)
 #	define be64toh(x) betoh64(x)
+#elif defined(__APPLE__)
+#       include <libkern/OSByteOrder.h>
+#       define be16toh(x) OSSwapBigToHostInt16(x)
+#       define be32toh(x) OSSwapBigToHostInt32(x)
+#       define be64toh(x) OSSwapBigToHostInt64(x)
+#       define htobe16(x) OSSwapHostToBigInt16(x)
+#       define htobe32(x) OSSwapHostToBigInt32(x)
+#       define htobe64(x) OSSwapHostToBigInt64(x)
 #endif
 
 #endif /* _KNOT_ENDIAN_H_ */