machines: use docker buildx (BuildKit) to build packages

`docker build` has been deprecated and is being replaced with
`docker buildx build`:
https://docs.docker.com/reference/cli/docker/buildx/

Vagrantfile

@@ -53,7 +53,7 @@ fi
 pacman --noconfirm -Su
 
 # Make sure Python, Docker and other needed packages are installed
-for PKG in docker gcc make pkgconf python
+for PKG in docker docker-buildx gcc make pkgconf python
 do
     pacman -Qqi "$PKG" > /dev/null || pacman --noconfirm -S "$PKG"
 done
@@ -84,7 +84,7 @@ cat > /etc/docker/daemon.json << EOF
 EOF
 systemctl enable --now docker
 gpasswd -a vagrant docker
-(docker images |grep -q '^archlinux ') || su vagrant -c 'docker build -t archlinux /vagrant/machines/archlinux'
+(docker images |grep -q '^archlinux ') || su vagrant -c 'docker docker-buildx build -t archlinux /vagrant/machines/archlinux'
 
 # Use vsyscall=emulate on the command line, for Debian 7 Wheezy
 if [ -e /boot/syslinux/syslinux.cfg ] && ! grep vsyscall=emulate /boot/syslinux/syslinux.cfg > /dev/null

machines/base_install/archlinux.sh

@@ -514,6 +514,7 @@ then
     pkg clinfo
     pkg codespell
     pkg cppcheck
+    pkg docker-buildx
     pkg docker-compose
     pkg earlyoom
     pkg flake8

machines/docker_build_run.sh

@@ -104,9 +104,9 @@ build_and_run() {
     then
         if "$DO_PRETEND"
         then
-            echo "docker build -f 'Dockerfile-$BASE_NAME' -t '$IMAGE_NAME' .."
+            echo "docker buildx build -f 'Dockerfile-$BASE_NAME' -t '$IMAGE_NAME' .."
         else
-            docker build -f "Dockerfile-$BASE_NAME" -t "$IMAGE_NAME" .. || return $?
+            docker buildx build -f "Dockerfile-$BASE_NAME" -t "$IMAGE_NAME" .. || return $?
         fi
     fi