[bug#30831] [PATCH] gnu: rust: Update rust from 1.22.1 release to 1.24.1

[Nikolai Merinov]

Hi Ludovic,

> Instead of incrementing the version number of the bootstrap binaries, do
> you think it would be an option to keep 1.22 and build 1.23 from it, or
> does that cargo/rust merge prevent it?

In rust 1.22 there already was possibility to build "cargo" from "rust"
repository, so suggested packages structures change can be used either
for old "rust" releases.

By default rust should be built with
https://github.com/rust-lang/rust/blob/1.24.1/src/stage0.txt versions of
rust and cargo. In most of cases this for "1.X.Y" release it want to use
"1.(X-1).0" version of rustc and "0.X.0" version of cargo. As result to
build release version of Rust compiler we should have previous release
of rust compiler.

Actually there is two ways to achieve this:
1. Constantly update bootsrap binaries version.
2. For each new release create new package. As result we'll be able to
use old rust release to build each new rust release. E.g. we can use
1.21.0 bootstrap binaries, then build 1.22.0 rust and use it to build
1.23.0 rust and then use it to build 1.24.1 rust.

Which way is preferable? 

Please do not merge my patch until I'll check Danny's report about
reproducability.

Regards,
Nikola