HelenOS sources

root/uspace/lib/posix/include/posix/

[..]
ctype.h dlfcn.h fcntl.h fenv.h fnmatch.h
getopt.h limits.h locale.h pthread.h pwd.h
signal.h stdio.h stdlib.h string.h strings.h
sys/ time.h ucontext.h unistd.h
[..]
HelenOS homepage, sources at GitHub