Improve linux32 wrapping and build with correct target platform
Two commits in this merge request.
Improve linux32 wrapping
Use linux32 as ENTRYPOINT so that commands passed to docker run are wrapped correctly. Also, use linux32 as SHELL to ensure the RUN commands when building the image are wrapped as well.
Build images with "--platform linux/amd64"
Otherwise docker assumes this image is supposed to run on x86 hosts and issues a warning when running on x86-64.