Add a single test runner

Running the whole test suite is not fun, and the magic incantations for
running a specific backend are too complicated to remember.

.gitlab-ci/run-single-test.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/sh
+#
+builddir=$1
+suite=$2
+unit=$3
+
+echo "** builddir: ${builddir}"
+echo "**    suite: ${suite}"
+echo "**     unit: ${unit}"
+
+export XDG_RUNTIME_DIR="$(mktemp -p $(pwd) -d xdg-runtime-XXXXXX)"
+
+weston --backend=headless-backend.so --socket=wayland-5 --idle-time=0 &
+compositor=$!
+
+export WAYLAND_DISPLAY=wayland-5
+
+meson test -C ${builddir} \
+            --print-errorlogs \
+            --setup=wayland \
+            --suite=${suite} \
+            --no-suite=failing \
+            --no-suite=flaky \
+            --no-suite=wayland_failing \
+            --no-suite=gsk-compare-broadway \
+            --verbose \
+            "${unit}"
+
+exit_code=$?
+kill ${compositor}
+
+exit ${exit_code}