`cfg(bootstrap)` docs don't say what it does

[camelid]

https://rustc-dev-guide.rust-lang.org/building/bootstrapping.html#why-does-only-libstd-use-cfgbootstrap

cc https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/rename.20.60cfg.28bootstrap.29.60.20to.20.60cfg.28stageN.29.60

[camelid]

It also misleadingly says that rustc only uses cfg(bootstrap) when adding internal lints for diagnostic items. That's not true; rustc also uses cfg(bootstrap) when feature gates that are used internally are renamed or removed.

[jyn514]

The docs for cfg(bootstrap) are here: https://rustc-dev-guide.rust-lang.org/building/bootstrapping.html#complications-of-bootstrapping. Maybe it would help to link there from the libstd section?

It also misleadingly says that rustc only uses cfg(bootstrap) when adding internal lints for diagnostic items. That's not true; rustc also uses cfg(bootstrap) when feature gates that are used internally are renamed or removed.

👍 I'll fix this.