Matrix image build : arm64 compatibility

podman-matrix/zz_build-images.sh

@@ -9,11 +9,20 @@ ensure_not_root
 
 buildfolder=/tmp/synapse-$$
 
+if [[ $(uname -i) == 'aarch64' ]]; then
+    buildkitarch='arm64'
+elif [[ $(uname -i) == 'x86_64' ]]; then
+    buildkitarch='amd64'
+else
+    # defaults to amd64
+    buildkitarch='amd64'
+fi
+
 if ! podman image exists localhost/matrixdotorg/synapse:${synapse_version}; then
     mkdir ${buildfolder} &&
     curl -sSfL -- "https://github.com/matrix-org/synapse/archive/refs/tags/${synapse_version}.tar.gz" | \tar xz --strip-components 1 -C ${buildfolder}/ && {
 	podman run -d --name buildkitd --privileged docker.io/moby/buildkit:latest &&
-	curl -sSLf https://github.com/moby/buildkit/releases/download/v0.9.3/buildkit-v0.9.3.linux-amd64.tar.gz | \
+	curl -sSLf https://github.com/moby/buildkit/releases/download/v0.9.3/buildkit-v0.9.3.linux-${buildkitarch}.tar.gz | \
 	    tar xz -C ~/ bin/buildctl &&
         ~/bin/buildctl --addr=podman-container://buildkitd build \
 		       --frontend dockerfile.v0 \