The other nice part of using LLVM is that you don't have to write a new Rust compiler for a new target, you just need to write the LLVM backend to convert LLVM

The other nice part of using LLVM is that you don't have to write a new Rust compiler for a new target, you just need to write the LLVM backend to convert LLVM IR to the target's assembly. That's substantially easier to do. So while LLVM doesn't support as many architectures as GCC yet it's far easier to add new architectures to it.