bug#43162: chgrp clears setgid even when group is not changed

[Bob Proulx]

Paul Eggert wrote:
> Karl Berry wrote:
> > I was on centos7.
> > 
> >      (I don't observe your problem on my Fedora 31 box, for example).
> > 
> > Maybe there is hope for a future centos, then.

Just another few data points...

I was able to recreate this issue on a CentOS 7 system running in a
tmpfs filesystem.  So that's pretty much pointing directly at the
Linux kernel behavior independent of file system type.

Meanwhile...  I can also recreate this on a Debian system with a Linux
4.9 kernel in 9 Stretch.  But not on 10 Buster Linux 4.19.  But once
again not on an earlier Linux 3.2 kernel.  3.2 good, 4.9 bad, 4.19 good.

Therefore this seems to be a Linux behavior that was the desired way,
then flipped to the annoying behavior way, then has flipped back again
later.  Apparently.  Anyway just a few data points.

Bob