reproduce (this is a W=1 build):
        # https://github.com/Rust-for-Linux/linux/commit/f008650c44ceb89d82441e79233d8e0f02fa9276
        git remote add rust https://github.com/Rust-for-Linux/linux
        git fetch --no-tags rust hrtimer-next
        git checkout f008650c44ceb89d82441e79233d8e0f02fa9276
        # 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