fix(build): create loop devices in container for efi.img mount

make_grub mounts the 4M efi.img with a loop device. The podman container
only had /dev/loop0 from the host, so losetup could not allocate a free
loop device and the build aborted at the EFI boot image step. Create
/dev/loop-control and /dev/loop0-15 before running buildiso.

build-iso-podman.sh

@@ -22,6 +22,11 @@ sudo podman run --rm --privileged --entrypoint sh \
     set -euo pipefail
     mkdir -p /var/lib/artools/buildiso
     mount -t tmpfs -o size=12G,exec,suid,dev tmpfs /var/lib/artools/buildiso
+    modprobe loop 2>/dev/null || true
+    [ -e /dev/loop-control ] || mknod -m 0660 /dev/loop-control c 10 237
+    for i in $(seq 0 15); do
+      [ -e "/dev/loop$i" ] || mknod -m 0660 "/dev/loop$i" b 7 "$i"
+    done
     /workspace/buildiso -p antergos
     echo "=== BUILD FINISHED ==="
     mkdir -p /workspace/iso-output