builder: Don't set up multiarch support multiple times
builder: Don't set up multiarch support multiple times

On Fedora 36, setting up support for building multiarch containers
in Docker using the multiarch/qemu-user-static container image
doesn't work as intended. Specifically, running

  $ docker run --platform=linux/aarch64 --rm alpine uname -m

doesn't produce any output and results in the SELinux error

  avc: denied { read } for comm="uname" path="/usr/bin/qemu-aarch64-static"

Installing the qemu-user and qemu-user-binfmt packages results in
being able to successfully run container images for foreign
architectures, but since we currently run the container-based
qemu-user setup unconditionally, that will get blown away as soon
as 'make builder-build' is executed and the build will not be able
to complete successfully.

Fix this by only running the setup step if things have not already
been configured earlier.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt