chroot_teardown: umount: race condition

When I run mkarchiso having in profiledef.sh the variable airootfs_image_type="erofs", the process fails at pacstrap with:

umount: _BUILD/x86_64/airootfs/sys/firmware/efi/efivars: target is busy.
umount: _BUILD/x86_64/airootfs/sys: target is busy.

The root cause is that at pacstrap the function chroot_teardown tries to unmount everything at once, being that sys is a mount within efivars.

Unmounting lazily solves it:

chroot_teardown() {
  if (( ${#CHROOT_ACTIVE_MOUNTS[@]} )); then
    umount -l "${CHROOT_ACTIVE_MOUNTS[@]}"
  fi
  unset CHROOT_ACTIVE_MOUNTS
}