/usr/include/x86_64-linux-gnu/bits
Edit: /usr/include/x86_64-linux-gnu/bits/endianness.h (273B)
#ifndef _BITS_ENDIANNESS_H
#define _BITS_ENDIANNESS_H 1
#ifndef _BITS_ENDIAN_H
# error "Never use
directly; include instead."
#endif
/* i386/x86_64 are little-endian. */
#define __BYTE_ORDER __LITTLE_ENDIAN
#endif /* bits/endianness.h */