relibc/include/machine/endian.h

#ifndef __MACHINE_ENDIAN_H__

#ifndef BIG_ENDIAN
    #define BIG_ENDIAN 4321
#endif

#ifndef LITTLE_ENDIAN
    #define LITTLE_ENDIAN 1234
#endif

#ifndef BYTE_ORDER
    #if defined(__IEEE_LITTLE_ENDIAN) || defined(__IEEE_BYTES_LITTLE_ENDIAN)
        #define BYTE_ORDER LITTLE_ENDIAN
    #else
        #define BYTE_ORDER BIG_ENDIAN
    #endif
#endif

#endif /* __MACHINE_ENDIAN_H__ */