reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?id=0942e6ae35b60b8f67ac961637e734b9cc34f225
        git remote add sysctl https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git
        git fetch --no-tags sysctl sysctl-testing
        git checkout 0942e6ae35b60b8f67ac961637e734b9cc34f225
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash fs/ kernel/