collect build artifacts

.gitlab-ci.yml

@@ -7,6 +7,10 @@ stages:
     - docker-build
   script:
     - python3 build-locally.py $CONFIG
+  artifacts:
+    expire_in: 1 month
+    paths:
+      - build_artifacts
 
 build_linux_64_python3.6.____cpython:
   extends: .build_template