reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/wpan/wpan-next.git/commit/?id=0f921404689398943257793f7240db239a23b609
        git remote add wpan-next https://git.kernel.org/pub/scm/linux/kernel/git/wpan/wpan-next.git
        git fetch --no-tags wpan-next staging
        git checkout 0f921404689398943257793f7240db239a23b609
        # 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