ci: cross compile on debian 13 to multiple architectures

Debian supports many architectures, and it is relatively easy to work
with multiarch packages, and finally `meson env2mfile` supports
generating cross files with the `--debarch` option.

Previously only native builds were done in the CI, so use debian to
build pipewire for multiple architectures.

Some packages are unfortunately not multiarch compatible, so a separate
container is built for every architecture.

.gitlab/ci/setup-debian-cross-container.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+
+set -ex
+
+packages=(
+	# libapparmor-dev
+	libasound2-dev
+	libavahi-client-dev
+	libavcodec-dev
+	libavfilter-dev
+	libavformat-dev
+	libbluetooth-dev
+	libcanberra-dev
+	libdbus-1-dev
+	libebur128-dev
+	libfdk-aac-dev
+	libffado-dev
+	libfftw3-dev
+	libfreeaptx-dev
+	libglib2.0-dev
+	libgstreamer1.0-dev
+	libgstreamer-plugins-base1.0-dev
+	libjack-jackd2-dev
+	liblc3-dev
+	liblilv-dev
+	libmysofa-dev
+	libopus-dev
+	libpulse-dev
+	libreadline-dev
+	libsbc-dev
+	libsdl2-dev
+	# libsnapd-glib-dev
+	libsndfile1-dev
+	libspandsp-dev
+	libssl-dev
+	libsystemd-dev
+	libudev-dev
+	libusb-1.0-0-dev
+	libvulkan-dev
+	libwebrtc-audio-processing-dev
+	libx11-dev
+	modemmanager-dev
+)
+
+arch="$1"
+
+export DEBIAN_FRONTEND=noninteractive
+
+sed -i \
+	's/^Components:.*$/Components: main contrib non-free non-free-firmware/' \
+	/etc/apt/sources.list.d/debian.sources
+
+dpkg --add-architecture "$arch"
+apt update -y
+
+pkgs=( "crossbuild-essential-$arch" )
+for pkg in "${packages[@]}"; do
+	pkgs+=( "$pkg:$arch" )
+done
+
+apt install -y "${pkgs[@]}"
+
+meson env2mfile --cross --debarch "$arch" -o "/opt/meson-$arch.cross"