[ricardobranco777]

POSIX.1-2024 adds close-on-fork: O_CLOFORK, FD_CLOFORK,
F_DUPFD_CLOFORK, SOCK_CLOFORK and MSG_CMSG_CLOFORK. Add them, along
with the system-specific F_DUP2FD_CLOFORK, F_DUP3FD and F_DUP3FD_SHIFT,
on the systems that implement them: FreeBSD 15.0, NetBSD 11.0,
OpenBSD 7.8, DragonFly BSD and illumos.

The zerrors files were edited by hand. mkerrors.sh already matches
these prefixes, so no generator change is needed. Regenerating would
require running each new release on every architecture and would pull
in many unrelated changes. The values were taken from these sources,
and are the same on every architecture of an OS:

FreeBSD    release/15.0.0  sys/sys/fcntl.h, sys/sys/socket.h
NetBSD     netbsd-11       sys/sys/fcntl.h, sys/sys/socket.h
OpenBSD    42a7be81bef7    sys/sys/fcntl.h, sys/sys/socket.h
DragonFly  dea249a60d18    sys/sys/fcntl.h, sys/sys/socket.h
illumos    3581f14f537c    uts/common/sys/fcntl.h, socket.h

The OpenBSD commit is the one that added close-on-fork, ahead of 7.8.

On FreeBSD and DragonFly, libc implements dup3 with F_DUP3FD and the
flags shifted by F_DUP3FD_SHIFT. Do the same in Dup3 when O_CLOFORK is
requested. Keep using F_DUP2FD and F_DUP2FD_CLOEXEC otherwise, so Dup3
keeps working on kernels without F_DUP3FD.

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