ci: Include gdm in image

gnome-shell depends on gdm's client library at runtime, but the
new pipeline-built image no longer provides it.

Add it back, but built it from source instead of using the Fedora
package, so we don't draw in all of gdm's runtime dependencies
(which includes a full GNOME session including gnome-shell).

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1590>

.gitlab-ci.yml

@@ -12,7 +12,7 @@ stages:
 .mutter.fedora:33:
   variables:
     FDO_DISTRIBUTION_VERSION: 33
-    FDO_DISTRIBUTION_TAG: '2020-11-20.0'
+    FDO_DISTRIBUTION_TAG: '2020-11-20.1'
     FDO_UPSTREAM_REPO: GNOME/mutter
     FDO_DISTRIBUTION_EXEC: |
       dnf install -y 'dnf-command(builddep)' &&
@@ -30,6 +30,14 @@ stages:
       dnf remove -y gnome-bluetooth-libs-devel &&
       dnf remove -y --noautoremove mutter mutter-devel &&
 
+      ./.gitlab-ci/install-meson-project.sh \
+          -Dlibaudit=disabled \
+          -Dplymouth=disabled \
+          -Dselinux=disabled \
+          -Dxdmcp=disabled \
+          https://gitlab.gnome.org/GNOME/gdm.git \
+          3.38.0 . &&
+
       dnf clean all
 
 default:

.gitlab-ci/install-meson-project.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+
+set -e
+
+if [[ $# -lt 3 ]]; then
+  echo Usage: $0 [options] [repo-url] [commit] [subdir]
+  echo  Options:
+  echo    -Dkey=val
+  exit 1
+fi
+
+MESON_OPTIONS=()
+
+while [[ $1 =~ ^-D ]]; do
+  MESON_OPTIONS+=( "$1" )
+  shift
+done
+
+REPO_URL="$1"
+COMMIT="$2"
+SUBDIR="$3"
+
+REPO_DIR="$(basename ${REPO_URL%.git})"
+
+git clone --depth 1 "$REPO_URL" -b "$COMMIT"
+pushd "$REPO_DIR"
+pushd "$SUBDIR"
+meson --prefix=/usr _build "${MESON_OPTIONS[@]}"
+ninja -C _build install
+popd
+popd
+rm -rf "$REPO_DIR"