reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git/commit/?id=eef9f6d8c36f7610b5f837e196692ec34842a400
        git remote add westeri-thunderbolt https://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git
        git fetch --no-tags westeri-thunderbolt next
        git checkout eef9f6d8c36f7610b5f837e196692ec34842a400

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/thunderbolt/