Allow execution of stage2 compiler to happen later
Currently cross-compiled bindists are rather incomplete since we can't run the stage2 compiler to build various utilities (e.g.
haddock). Ideally we would be able to run a build up to the point where we need to run host code, package up the build tree, and finish the build on the host. There are a number of challenges that this brings, but it will ultimately make it far easier to build proper non-Linux/amd64 bindists on CircleCI (#14949 (closed)).