That's what I don't get. I looked through the available documentation briefly and didn't see any mention that this is intended to be a `mrustc`; it really seems

That's what I don't get. I looked through the available documentation briefly and didn't see any mention that this is intended to be a `mrustc`; it really seems to want to be a `rustc`. I'm not aware of other GCC frontends being less than complete compilers for their respective languages, and while I think that "rust without borrowck" is an interesting point in design space (discriminated unions, generics, macros, traits, closures), "rust without borrowck" is not rust.