reproduce (this is a W=1 build):
        git remote add chrome-os https://chromium.googlesource.com/chromiumos/third_party/kernel
        git fetch --no-tags chrome-os chromeos-6.6
        git checkout 71e4fcb288df366078213ba4fcf976f12a14d5e2
        # save the config file
        make W=1 ARCH=x86_64 olddefconfig
        make W=1 ARCH=x86_64