I've read that in the case of Go, Googlers develop in the public repo of Go, which is periodically synced back into the Google tree. You can definitely see tha

I've read that in the case of Go, Googlers develop in the public repo of Go, which is periodically synced back into the Google tree. You can definitely see that Google uses a completely different build system than mainstream Go by the state of the mainstream Go build system though.