reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git/commit/?id=4d8681660c8aad5c0d6c0f3be279e413ea917cb3
        git remote add vireshk https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git
        git fetch --no-tags vireshk rust/cpufreq-dt
        git checkout 4d8681660c8aad5c0d6c0f3be279e413ea917cb3
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash CLIPPY=1 rustdoc