Auto merge of #48405 - kennytm:autotoolstate-follow-up, r=Mark-Simulacrum
Auto-toolstate management follow-up.
Tracking comment: https://github.com/rust-lang/rust/issues/45861#issuecomment-367302777
* Fixed rust-lang-nursery/rust-toolstate#1, a proper link to the PR will be included.
* Fixed rust-lang-nursery/rust-toolstate#2, a comment will be posted to the PR if the toolstate changed
* Toolstate regression will be rejected at the last week of the 6-week cycle (currently entirely date-based).
* Implemented https://internals.rust-lang.org/t/the-current-submodule-setup-is-not-tenable/6593, moved doc tests of Nomicon, Reference, Rust-by-Example and The Book to the "tools" job and thus allowed to fail like other external tools.