Rust front-end merged in GCC trunk
I have asked this question before, but why write an entirely new frontend, which is an enormous task if you want to reach a similar quality to rustc?  
rustc_codegen_gcc¹ adds gcc as a backend to rustc alongside llvm, miri and (wip) cranelift. As a result, it always works with the newest version of rust and is already nearly complete after less work.¹https://github.com/rust-lang/rust/tree/master/compiler/rustc...