HelenOS sources
_Exit 86 common/include/stdlib.h extern void _Exit(int) __attribute__((noreturn));
_Exit 86 kernel/generic/common/include/stdlib.h extern void _Exit(int) __attribute__((noreturn));
_Exit 86 uspace/lib/c/common/include/stdlib.h extern void _Exit(int) __attribute__((noreturn));
_Exit 136 uspace/lib/c/generic/stdlib.c _Exit(status);
_Exit 184 uspace/lib/c/generic/stdlib.c _Exit(status);
_Exit 86 uspace/lib/posix/include/common/stdlib.h extern void _Exit(int) __attribute__((noreturn));
HelenOS homepage, sources at GitHub