Debian/oldstable docker container for packaging (#942)

This adds dockerized build stances to .gitlab-ci.yml. They will run only in scheduled builds (i.e. once per day at night) or upon special request (through secret GUI button). They shall ensure that at any time we are ready to generate binary installers.

This resolves #942 (closed).

devtools/deploy/linux/Dockerfile.debian.oldstable

@@ -10,9 +10,12 @@ RUN apt-get install -y \
   libboost-dev libboost-iostreams-dev \
   libboost-program-options-dev libboost-regex-dev \
   libcerf-dev qt6-base-dev/bullseye-backports qt6-svg-dev/bullseye-backports \
-  curl git tk-dev ccache xvfb patchelf \
+  curl git tk-dev ccache xvfb \
   zlib1g-dev libffi-dev libssl-dev libbz2-dev libreadline-dev libsqlite3-dev liblzma-dev
 
+# auditwheel requires patchelf >= 0.14; Debian/oldstable only has 0.12.
+RUN git clone https://github.com/NixOS/patchelf.git && cd patchelf && ./bootstrap.sh && ./configure && make && make check && make install
+
 ENV HOME /root
 RUN curl https://pyenv.run | bash
 ENV PYENV_ROOT="/root/.pyenv"