Explain stages in terms of the compiler currently running (take N+1) (#857)
Explain stages in terms of the compiler currently running (take N+1) (#857)

* Explain stages in terms of the compiler currently running

- Address some confusing points
  + stage N+1 -> stage N artifacts
  + Use more likely examples of an ABI break
  + stage N -> stage N compiler

- Mention why rustc occasionally uses `cfg(bootstrap)`
- Note that stage1 is built using two different versions

- Add lots of examples
  + `test src/test/ui` and `test compiler/rustc` run different compilers 😢
  + Separate examples of what to do from examples of what not to do

- 'ship stage 1 artifacts' -> 'ship stage 2 compiler'

  This is hopefully less confusing.

* build -> x.py build

* Add section on build artifacts

* Improve wording

Co-authored-by: Camelid <085dfe3d9dac499255796a5887eda9e32e004b34@users.noreply.github.com>

* uplifted -> assembled

Co-authored-by: Camelid <085dfe3d9dac499255796a5887eda9e32e004b34@users.noreply.github.com>
rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide