xlc_r -c -I./Modules/expat -DNDEBUG -O -qalias=noansi -qmaxmem=-1 -I./Include/internal -I. -I./Include -o Modules/expat/xmlrole.o ./Modules/expat/xmlrole.c
"./Modules/_hacl/include/krml/lowstar_endianness.h", line 152.4: 1506-205 (S) #error "Please define __BYTE_ORDER__!"
xlc_r -c -I./Modules/expat -DNDEBUG -O -qalias=noansi -qmaxmem=-1 -I./Include/internal -I. -I./Include -o Modules/expat/xmltok.o ./Modules/expat/xmltok.c

AIX doesn't have endian.h file. With XLC compiler __BYTE_ORDER__ is also not available.
AIX is always big-endian. So probably "defined(_AIX)" is needed in the generic big-endian fallback code in lowstar_endianness.h.

Linked PRs

• gh-102204: Fix endianness issue in AIX #102206