reproduce (this is a W=1 build):
        git remote add dwmw2 git://git.infradead.org/users/dwmw2/linux
        git fetch --no-tags dwmw2 hardpps-filter-soak
        git checkout eb57681e2ecf93179ad3e658a98646183bfb9fdf

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um SUBARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=um SUBARCH=i386 SHELL=/bin/bash drivers/pps/clients/