Add missing POSIX O_CLOFORK

[Ricardo Branco]

Hi!  The flag landed on FreeBSD.  I updated the PR with manpage fixes.

Best,

On 7/3/25 5:24 PM, Matthew Dillon wrote:
> Hi Ricardo!  It looks really good!  I'll get it tested (the exec 
> part), and checked for security, and committed in the next day or 
> two.   We don't need to commit more than basic tests as we don't 
> really have a strong testing suite anyway.
>
> -Matt