reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git/commit/?id=90347d82e4d3fa1705e513f04066f7c9c2b34694
        git remote add jack-fs https://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git
        git fetch --no-tags jack-fs for_next
        git checkout 90347d82e4d3fa1705e513f04066f7c9c2b34694
        # apt-get install llvm-dev

        # save the config file
        make W=1 ARCH=i386 olddefconfig
        make W=1 ARCH=i386 
        make W=1 headers_install
        make W=1 -C tools/testing/selftests