Enable limiting of compression threading

The xz compression is currently being configured to use a number of worker threads equal to the processors on the system being used. This is generally OK, however in some instances we compile packages on large machines, with as many as 160 CPU cores.

This fix was taken from linux@c3501dad

https://phabricator.apertis.org/T9633

Signed-off-by: Walter Lozano walter.lozano@collabora.com