add container-based development shell

It does not work with the graphical QEMU output but can build all
binaries.

Containerfile

@@ -0,0 +1,14 @@
+FROM debian@sha256:cd50e36013f749a1f86c6369b873e1ad607335480dc4bc2905396ec17ab0ce02
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        gcc \
+        g++ \
+        make \
+        flex \
+        bison \
+        gawk \
+        perl \
+        dialog \
+        libncurses-dev \
+        qemu-system-x86

container.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env sh
+
+# Run a shell inside of the container-based development environment.
+#
+# However, to see and use the QEMU UI, you need to run QEMU outside of the container.
+
+set -eu
+
+cd "$(dirname "$0")"
+
+if podman --version; then
+	cmd=podman
+else
+	cmd=docker
+fi
+
+"$cmd" build --tag=moslab .
+"$cmd" create --interactive --tty --name=moslab --volume="$(pwd)":"$(pwd)" \
+	--workdir="$(pwd)" moslab bash || true
+"$cmd" start --attach --interactive moslab