That said, there are some open source pieces to help. Facebook open sourced their mercurial stuffs so you can get version control at scale (and before then you just use perforce). Google open sourced bazel. Google open sourced some parts of the underlying infra behind code search, but not enough to really work properly. And of course lower level there's a plethora of reasonable db offerings, etc.
It would still require a lot of glue though.