QGC is not using Jenkins actively for QA or binary building and is using QMake as build system (not CMake as Jenkins is). Maintaining two ways of doing things dilutes the limited time available for QA and CI maintenance and Travis / Github actions plus AppVeyor work perfectly fine.

Removing old, no longer used branches (and launching a new build to check the results)

from jenkins docs: When applied at the top-level of the pipeline block no global agent will be allocated for the entire Pipeline run and each stage section will need to contain its own agent section.

Use runtime discovery of cpu core count