Fixes rust-lang#24372

Replaced by adding extra imports, adding hidden code (`# ...`), modifying
examples to be runnable (sorry Homura), specifying non-Rust code, and
converting to should_panic, no_run, or compile_fail.

Remaining "```ignore"s received an explanation why they are being ignored.

…ocks.

…bank

Remove most "```ignore" doc tests.

Unconditional ` ```ignore ` doc tests lead to outdated examples (e.g. rust-lang#42729 (comment)). This PR tries to change all existing ` ```ignore ` tests into one of the following:

* Add import and declarations to ensure the code is run-pass
* If the code is not Rust, change to ` ```text `/` ```sh `/` ```json `/` ```dot `
* If the code is expected compile-fail, change to ` ```compile_fail `
* If the code is expected run-fail, change to ` ```should_panic `
* If the code can type-check but cannot link/run, change to ` ```no_run `
* Otherwise, add an explanation after the ` ```ignore `

The `--explain` handling is changed to cope with hidden lines from the error index.

Tidy is changed to reject any unexplained ` ```ignore ` and ` ```rust,ignore `.

Redox: Use create() instead of open() when setting env variable

See redox-os/kernel#25.

…meGomez

add extended information for E0562; impl Trait can only be a return type

r? @GuillaumeGomez

…on-stderr, r=alexcrichton

Print -Zincremental-info to stderr instead of stdout.

Fixes rust-lang#42583.

The [cargo-incremental](https://github.com/nikomatsakis/cargo-incremental) tool probably does not need to be updated. It already merges stdout and stderr before parsing the compiler's output.

r? @alexcrichton

…excrichton

Ensure Guard types impl Display & Debug

Fixes rust-lang#24372

Fix ref as mutable ref in std::rc::Rc doc

Set CXX_<target> in bootstrap

I came across this trying to cross-compile rustc for Redox. It was also mentioned in a comment on rust-lang#42206, but doesn't seem to have been corrected.

…nt, r=Mark-Simulacrum

change span label for E0435

r? @Mark-Simulacrum