Add Guix step including bootstrap bin, build guix, build iso and fix some small bug

steps-guix/improve/guix-build-iso.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set -e
+
+. /steps/bootstrap.cfg
+. /steps/env
+
+daemon_socket="/var/guix/daemon-socket/socket"
+out_dir="/external/guix-images"
+
+if [ ! -S "${daemon_socket}" ]; then
+    echo "guix-daemon socket is missing: ${daemon_socket}" >&2
+    echo "Run improve/guix-daemon-and-pull.sh first." >&2
+    exit 1
+fi
+
+mkdir -p "${out_dir}"
+
+iso_store_path="$(guix system image \
+    --system=x86_64-linux \
+    -t iso9660 \
+    -e '(@@ (gnu system install) installation-os)' \
+    --no-substitutes)"
+
+if [ ! -e "${iso_store_path}" ]; then
+    echo "guix system image did not return a valid path: ${iso_store_path}" >&2
+    exit 1
+fi
+
+ln -sfn "${iso_store_path}" "${out_dir}/guix-system-install-x86_64.iso"