test: make container Valgrind runnable

Dockerfile

@@ -26,6 +26,15 @@ RUN pacman -Syu --noconfirm --needed \
 	dbus \
 	&& pacman -Scc --noconfirm
 
+RUN export DEBUGINFOD_URLS=https://debuginfod.archlinux.org \
+	&& buildid="$(readelf -n /usr/lib/ld-linux-x86-64.so.2 | sed -n 's/.*Build ID: //p')" \
+	&& test -n "$buildid" \
+	&& debugdir="/usr/lib/debug/.build-id/$(printf '%.2s' "$buildid")" \
+	&& mkdir -p "$debugdir" \
+	&& install -m 0644 "$(debuginfod-find debuginfo /usr/lib/ld-linux-x86-64.so.2)" \
+		"$debugdir/${buildid#??}.debug" \
+	&& rm -rf /root/.cache/debuginfod_client
+
 RUN printf "egrep='grep -E'\n" > /usr/lib/plan9/config
 RUN dbus-uuidgen --ensure=/etc/machine-id