If `settings.buildDir` cannot be written to, because we are in a chroot
store, unprivileged or anything.
We can and should always gracefully fallback to a *secure* location
inside of /tmp, i.e. `/tmp/<a directory under 0700>/<our temporary
directory for build under 0700>/...`.
This does not reintroduce CVE-2025-52991 because we are creating a
directory in-between compared to creating only ONE level of directory.
Fixes#876.
Change-Id: Ie521202923f763225e1901ab1b9b6c6132aaf548
Signed-off-by: Raito Bezarius <raito@lix.systems>