Description:


Additional info:
* devtools 20191016-1

Steps to reproduce:
* make sure /var/lib/archbuild is not on btrfs (in which case this issue doesn't exist)
* run extra-x86_64-build -c
* while it's running pacstrap and has /var/lib/archbuild/extra-x86_64/root/run mounted, another user logs in, thus creating a new mountpoint /run/user/$uid that propagates into /var/lib/archbuild/extra-x86_64/root/run/user/$uid
* run extra-x86_64-build -c again later, you'll see the error:

$ extra-x86_64-build -c
==> Creating chroot for [extra] (x86_64)...
-> Deleting chroot copy 'root'...
rm: skipping '/var/lib/archbuild/extra-x86_64/root/run', since it's on a different device
rm: skipping '/var/lib/archbuild/extra-x86_64/root/run', since it's on a different device
==> ERROR: Working directory '/var/lib/archbuild/extra-x86_64/root' already exists
==> ERROR: Aborting...

I suggest adding `unshare -m` in front of the `pacstrap` command.