reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/commit/?id=a7bcb4be2c8e4c7111e65ae0ce9ffebec202a2a3
        git remote add jpoimboe https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git
        git fetch --no-tags jpoimboe klp-build
        git checkout a7bcb4be2c8e4c7111e65ae0ce9ffebec202a2a3
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um prepare