Improve Ubuntu engineering build CI loop for Linaro Ubuntu

Speed up CI loop by crossbuilding slow jobs and taking control of our own repositories.

Cross-Build: Tools and package fixes improvements for minimal bootstrap support for Linaro Ubuntu

Remaining fixes and improvements for minimal bootstrap support using cross-build with multi-arch. This is needed to support the remaining work necessary to be able to cross-bootstrap a rootfs, which will be used during ARMv8 bootstrap.

XDeb Cross-Compilation Environment for Ubuntu

Starting from the Chromiumos-Build, we should provide a new XDeb tool allowing easy *true* cross-compilation. * rebranding of chromiumos-build * ignoring/breaking build-deps loops for single builds * testing against a subset of main, providing a default config to match non-crossable .debs