I guess this doesn't solve the bootstrapping issue.

Neither does this project of it contains parts that needs a rust compiler to be bootstrapped

It is the Rust compiler, the article describes how the (Rust) compiler is first compiled without the Rust code in it and then used to bootstrap the final version which does have the Rust code in it

incorrect, this is a re-implementation of rust by designed to be included in gcc, not the original rust compiler.

You didn't read the part about compiling with the borrow checker turned off?