reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/linux.git/commit/?id=63449354e053b5d2f3e6a4a9502624312ce75ccc
        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 63449354e053b5d2f3e6a4a9502624312ce75ccc
        # 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