Formerly, in this case an error was returned but the pid was also returned
to the application, requiring the application to use unspecified behaviour
(the returned pid in error situations) to avoid zombies.
Now, reap the zombie and do not return the pid.
MFC after: 2 weeks
* retry various system calls on EINTR
* retry the rest after a short read (common if there is more than about 1K
of output)
* block SIGCHLD like system(3) does (note that this does not and cannot
work fully in threaded programs, they will need to be careful with wait
functions)
PR: 90580
MFC after: 1 month