{"ast_node_type":"variable","tokens":[{"end":99,"kind":"keyword","start":0,"text":"let"}]}
    let llvm_arch = sess.target.llvm_target.split_once('-').expect("LLVM target must have arch").0;
    // `sess.target.arch` (`target_arch`) is not detailed enough.
    let target_os = &*sess.target.os;