It's more the third build system. IIRC google1 (I can't remember the actual directory name, maybe //google/) used Makefiles and Makefile generators. IIRC there

It's more the third build system. IIRC google1 (I can't remember the actual directory name, maybe //google/) used Makefiles and Makefile generators. IIRC there is a small amount of still-live code here. google2 failed fairly quickly. google3 is blaze/bazel and is where almost all development is today. All three trees are actually in the same source control "depot". If you read enough of their papers this is actually detailed there but spread across different papers.