This makes the docker image contain a PGO optimized compiler,
without needing to redo all of the PGO build stages in docker.
This reverts commit 8f42112719,
and fixes building the multiplatform image in a simpler way.
Instead of doing two separate builds, with separate Dockerfiles,
just do one multiplatform build of one Dockerfile, which
docker runs serially, for each one of the included architectures,
just packaging the prebuilt toolchains in the docker image.
Martin Storsjö
04bc2bc1c5