I don't know what point you're trying to make but your question was what's an alternative to llvm. People writing compilers always used C89 or a version of it (C11 allows an easier atomic implementation). There's a lot more C89 compilers than backends that llvm supports. When I was writing arduino code clang/llvm couldn't generate the AVR code for the board. The default toolchain was gcc with an AVR backend. IIRC it had optimizations and was the only reasonable compiler I could use. There's nothing wrong using C as your backend