Fix first run logic for os build script

Move initialization of multi-platform support to the bootstrap stage so
that building an arm64 root filesystem works out of the box on amd64.
Also correctly handle directories that don't exist on the first run.

packages/os/build.sh

@@ -23,11 +23,15 @@ function bootstrap() {
         dev="true"
     fi
 
-    if [ -z "${SKIP_ARM64:-}" ]; then 
+    # Enable QEMU/binfmt-based multi-platform support for building arm64 on
+    # amd64 or vice versa, e.g. to build for Pi 5 on an x86 system.
+    docker run --privileged --rm tonistiigi/binfmt --install all
+
+    if [ -z "${SKIP_ARM64:-}" ]; then
         build_root_fs arm64 "${release}"
         build_rugpi_images
     fi
-    if [ -z "${SKIP_AMD64:-}" ]; then 
+    if [ -z "${SKIP_AMD64:-}" ]; then
         build_root_fs amd64 "${release}"
     fi
 
@@ -87,36 +91,32 @@ function build_rugpi_images() {
     mkdir -p rugpi/build
     # Copy the root filesystem previously build with Docker.
     cp build/umbrelos-arm64.tar rugpi/build/umbrelos-base.tar
-
-    # Enable `binfmt`-based emulation for `arm64`.
-    docker run --privileged --rm tonistiigi/binfmt --install all
-
     # Copy `/etc/hostname` and `/etc/hosts` such that Rugpi can fix them.
     cp overlay-common/etc/{hostname,hosts} rugpi/recipes/fix-overlay/files
 
     pushd rugpi
     # Clean Rugpi cache to get a clean build.
-    rm -rf .rugpi
+    rm -rf .rugpi || true
     # Bake both images.
     if [ -z "${SKIP_PI4:-}" ]; then 
         ./run-bakery bake image pi4 build/umbrelos-pi4.img
         # Move image to global build directory.
-        mv build/umbrelos-pi4.img ../build/umbrelos-pi4.img
+        mv -f build/umbrelos-pi4.img ../build/umbrelos-pi4.img
     fi
     if [ -z "${SKIP_PI5:-}" ]; then 
         ./run-bakery bake image tryboot build/umbrelos-tryboot.img
         # Move image to global build directory.
-        mv build/umbrelos-tryboot.img ../build/umbrelos-pi5.img
+        mv -f build/umbrelos-tryboot.img ../build/umbrelos-pi5.img
     fi
     popd
 }
 
 # This will run inside a container when the --bootstrapped flag is passed
 function bootstrapped() {
-    if [ -z "${SKIP_ARM64:-}" ] && [ -z "${SKIP_MENDER:-}" ]; then 
+    if [ -z "${SKIP_ARM64:-}" ] && [ -z "${SKIP_MENDER:-}" ]; then
         build_raspberrypi_mender_artifact
     fi
-    if [ -z "${SKIP_AMD64:-}" ]; then 
+    if [ -z "${SKIP_AMD64:-}" ]; then
         build_x86_artifacts
     fi
 }
@@ -230,4 +230,4 @@ then
     bootstrapped
 else
     bootstrap $@
-fi
+fi