This is xnu-8019. See this file in:
Directory listing for xnu-8019//libsyscall/custom
SYS.h
__fork.s
__getpid.s
__gettimeofday.s
__kdebug_trace_string.s
__lseek.s
__pipe.s
__ptrace.s
__sigaltstack.s
__sigreturn.s
__syscall.s
__thread_selfid.s
__thread_selfusage.s
__vfork.s
custom.s
dummy.c
errno.c