reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git/commit/?id=368990a7fe30737c990f628a60d26d9854a9e690
        git remote add xen-tip https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git
        git fetch --no-tags xen-tip linux-next
        git checkout 368990a7fe30737c990f628a60d26d9854a9e690
        # 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