gitlab-ci: add script to download sccache

.gitlab/ci/sccache.sh

+#!/bin/sh
+
+set -e
+
+readonly version="0.2.12"
+readonly sha256sum="26fd04c1273952cc2a0f359a71c8a1857137f0ee3634058b3f4a63b69fc8eb7f"
+readonly filename="sccache-$version-x86_64-unknown-linux-musl"
+readonly tarball="$filename.tar.gz"
+
+cd .gitlab
+
+echo "$sha256sum  $tarball" > sccache.sha256sum
+curl -OL "https://github.com/mozilla/sccache/releases/download/$version/$tarball"
+sha256sum --check sccache.sha256sum
+tar xf "$tarball"
+mv "$filename/sccache" .