Alternative to cl/4661 discussed in #1044.
It can be assumed that `$tmpdir/build-top` can be created safely without
any risk, this way, we don't need to reuse the random directory creation
primitive.
Fixes#1044.
Change-Id: Iec52477f3047fc40959b183c607312d5a40fc8c9
Signed-off-by: Raito Bezarius <raito@lix.systems>
