uclibc-ng/libc/sysdeps/linux/xtensa/bits/endian.h

#ifndef _ENDIAN_H
# error "Never use <bits/endian.h> directly; include <endian.h> instead."
#endif

/* Xtensa can be either big or little endian.  */
#ifdef __XTENSA_EB__
# define __BYTE_ORDER __BIG_ENDIAN
#else
# define __BYTE_ORDER __LITTLE_ENDIAN
#endif