[PATCH v7] linux: use PIDFD_GET_INFO ioctl for pidfd_getpid() if available

[Florian Weimer]

* Luca Boccassi:

> Unfortunately it doesn't help with existing kernels though. Is there a
> test macro that can be used to check for either/or?

I've used

  if (errno != EREMOTE)
    TEST_COMPARE (errno, ESRCH);

to cover two possible alternatives.

Thanks,
Florian