In SERVER-27505, we added support for topsorting our libraries. As part of that change, we stopped sorting the results reported by the scanner:

https://github.com/mongodb/mongo/commit/190dcaab71bcca027954e227ac73a36958aab762#diff-d90fa2623f9db54079c913e56e6183e0R188

That caused the dependency orders to change run-to-run, unless you were building with --implicit-cache. Since most users do build that way, we didn't notice.

The solution is to simply append the results in the stable order returned by __get_libdeps.