This project doesn’t have that as a goal. In fact, it doesn’t even have “Rust to C compiler” as a goal. https://github.com/FractalFir/rustc_codegen_clr:

“ The project aims to provide a way to easily use Rust libraries in .NET. It comes with a Rust/.NET interop layer, which allows you to easily interact with .NET code from Rust

[…]

While .NET is the main focus of my work, this project can also be used to compile Rust to C, by setting the C_MODE enviroment flag to 1.

This may seem like a strange and unrelated feature, but the project was written in such a way that this is not only possible, but relatively easy.”

It also doesn’t mention for which version of C it produces code. That may or may not hinder attempts to use this to run rust on obscure platforms.