reproduce (this is a W=1 build):
        git remote add arm git://git.armlinux.org.uk/~rmk/linux-arm.git
        git fetch --no-tags arm aarch64/hotplug-vcpu/v6.7
        git checkout 65e760d9bf772f49ab4398c1a529816d030d4c11
        # 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