There are some declaration order changes, and a few test classes switched from `struct` to `class`. However, this PR is mostly adopting `_` naming of private member variables due to the shift in naming style. None of what's here should have behavior impacts, it should just be style.
Note, there are a lot of things that *look* like they could be accessor-named, but I'm not doing that in this change. Happy to do it separately if you want me to do another PR focused on it.
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
This should clean up our top level directory and the build patterns.
No non-mechanical edits here. Just injecting `toolchain/` and
`TOOLCHAIN_` and then running formatting tools.