Use Xenial as the build image's base distribution

Since Xenial has the oldest glibc (2.23) of all the active distributions, this
attempts to construct a build image based on that. The Dockerfile here was built
by recursively expanding the `FROM` lines until reaching
`buildpack-deps:bionic-curl` and then changing that to `xenial`. Everything else
is the same.

Part of https://github.com/vector-im/riot-web/issues/13553

dockerbuild/Dockerfile

@@ -1,4 +1,42 @@
-FROM electronuserland/builder:12
+FROM buildpack-deps:xenial-curl
+
+ENV DEBIAN_FRONTEND noninteractive
+
+RUN curl -L https://yarnpkg.com/latest.tar.gz | tar xvz && mv yarn-* /yarn && ln -s /yarn/bin/yarn /usr/bin/yarn
+RUN apt-get -qq update && apt-get -qq dist-upgrade && \
+  # add repo for git-lfs
+  curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | bash && \
+  # git ssh for using as docker image on CircleCI
+  # python for node-gyp
+  # rpm is required for FPM to build rpm package
+  # libsecret-1-dev and libgnome-keyring-dev are required even for prebuild keytar
+  apt-get -qq install --no-install-recommends qtbase5-dev bsdtar build-essential autoconf libssl-dev gcc-multilib g++-multilib lzip rpm python libcurl4 git git-lfs ssh unzip \
+  libsecret-1-dev libgnome-keyring-dev \
+  libopenjp2-tools && \
+  # git-lfs
+  git lfs install && \
+  apt-get purge -y --auto-remove && rm -rf /var/lib/apt/lists/*
+
+COPY test.sh /test.sh
+
+WORKDIR /project
+
+# fix error /usr/local/bundle/gems/fpm-1.5.0/lib/fpm/package/freebsd.rb:72:in `encode': "\xE2" from ASCII-8BIT to UTF-8 (Encoding::UndefinedConversionError)
+# http://jaredmarkell.com/docker-and-locales/
+# http://askubuntu.com/a/601498
+ENV LANG C.UTF-8
+ENV LANGUAGE C.UTF-8
+ENV LC_ALL C.UTF-8
+
+ENV DEBUG_COLORS true
+ENV FORCE_COLOR true
+ENV NODE_VERSION 12.16.1
+
+# this package is used for snapcraft and we should not clear apt list - to avoid apt-get update during snap build
+RUN curl -L https://nodejs.org/dist/v$NODE_VERSION/node-v$NODE_VERSION-linux-x64.tar.gz | tar xz -C /usr/local --strip-components=1 && \
+  unlink /usr/local/CHANGELOG.md && unlink /usr/local/LICENSE && unlink /usr/local/README.md && \
+  # https://github.com/npm/npm/issues/4531
+  npm config set unsafe-perm true
 
 ENV RUSTUP_HOME=/usr/local/rustup \
     CARGO_HOME=/usr/local/cargo \