Draft: tidy/strip: run file stripping in parallel to speed up file stripping

Collecting the debug symbols usually takes a chunk of time during package building and running this on the available number of cores speeds this up by a significant margin.

Part of the idea is taken from the rpm code. https://github.com/rpm-software-management/rpm/blob/rpm-4.20.x/scripts/brp-strip

Signed-off-by: Morten Linderud morten@linderud.pw