reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/commit/?id=ffe1588178d5bb71c58361cb84cc3f4342f82100
        git remote add hyperv https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git
        git fetch --no-tags hyperv hyperv-next-staging
        git checkout ffe1588178d5bb71c58361cb84cc3f4342f82100
        # 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