This change adds experimental prefix builds to the Flatcar SDK.
Prefix builds use a custom sys prefix path and emerge all binaries and
runtime dependencies into that prefix.
This path can then e.g. be shipped as a portable sysext since it
includes all dependencies, and has libraries at a custom path so these
do not conflict with libraries on target systems.
Prefix uses a staging environment (path) featuring a full-blown
development environment, and a "final" environment for installing.
Staging and final need to be created using setup_prefix first,
which will also create an emerge wrapper to emerge ebuilds into staging
and subsequently final. The root fs in final may then e.g. be used to
create a distro independent, portable sysext.
Co-authored-by: James Le Cuirot <chewi@gentoo.org>
Co-authored-by: Jeremi Piotrowski <jpiotrowski@microsoft.com>
Co-authored-by: Thilo Fromm <thilofromm@microsoft.com>
