Update rust version

[bitwave]

Is it possible to lift the rust dependency from nightly-2019-07-08 to a newer version? This is two (!) years old?

[mssun]

Yes, what we should do is following:

• Port changes of the Rust std/compiler-builtin/etc to a recent versions
• Upgrade the toolchain requirements of Rust

This needs to be done at the same time because the std code can only be compiled in a certain range versions of the Rust toolchain. (E.g., if std use a new language feature, it needs to be compile with the newer toolchain)

[bitwave]

I tried to do this by myself, but I got stuck at the std lib parts, where many things are missing/changed from this old version to the new one. Many parts look like boilerplate code to me...

[mssun]

@bitwave the toolchains has been updated to nightly-2021-09-20. Thanks!