Now I really have broken the build

Last time I broke the build it auto-fixed itself. Now I think I've really broken it.

Warning, treated as error:
/home/buildbot/llvm-build-dir/llvm-sphinx-docs/llvm/src/llvm/docs/TableGen/BackGuide.rst:document isn't included in any toctree
ninja: build stopped: subcommand failed.

I'm not sure what the problem is. When I've added a new document in the past, I didn't register it in any Cmake file. But that sounds like what the problem is now.

If you respond, I'd appreciate knowing what the steps are to fix a broken build. I'm not sure what I need to push.