Add support for multi-arch containers

Create the kas and kas-isar containers also for arm64. This allows using
them for arm-native builds, e.g. in AWS instances.

We need to drop a couple of packages from arm64 images which do not
exist on that arch. If the kas image is usable for Yocto builds is
untested, though. The Isar image works.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

Dockerfile

@@ -2,6 +2,7 @@
 
 FROM debian:buster-slim
 
+ARG TARGETPLATFORM
 ARG DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update && \
@@ -10,14 +11,17 @@ RUN apt-get update && \
 ENV LANG=en_US.utf8
 
 RUN apt-get install --no-install-recommends -y \
-        gawk wget git-core diffstat unzip texinfo gcc-multilib \
+        gawk wget git-core diffstat unzip texinfo \
         build-essential chrpath socat cpio python python3 python3-pip python3-pexpect \
         xz-utils debianutils iputils-ping python3-git python3-jinja2 libegl1-mesa libsdl1.2-dev \
         pylint3 xterm \
         python3-setuptools python3-wheel python3-yaml \
         gosu lsb-release file vim less procps tree tar bzip2 zstd bc tmux libncurses-dev \
-        dosfstools mtools parted syslinux \
+        dosfstools mtools parted \
         git-lfs mercurial iproute2 ssh-client curl rsync gnupg awscli && \
+    if [ "$TARGETPLATFORM" = "linux/amd64" ]; then \
+        apt-get install --no-install-recommends -y gcc-multilib syslinux; \
+    fi && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*