Rust and GCC, two different ways

> Intel and Embarcadero likewise shipped Clang. Because again, they couldn't keep up.

This was true for Arm too; With ARMCC 6, they moved to Clang, extending it to maintain frontend/cmdline compatibility with the older stuff. But ARMCC, as shipped, remains as proprietary as ever.

(While Arm contributes a lot to upstream GCC and LLVM, what landed upstream tended to lag significantly from what they shipped in ARMCC. Granted, that policy could have changed in the three years since I worked there...)