I think the claim is that GCC supports a few obscure platforms that LLVM doesn't. Don't ask me which, that is just the claim that I heard multiple times. So it's not Rust that limits platforms, but LLVM. And they say the GCC backend efforts of Rust are meant to deal with that.

> Don't ask me which

There are many. Two big ones are Alpha and PA-RISC. NetBSD and Linux continue to support both. Linux distro choices are pretty much limited to Gentoo though.