reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc.git/commit/?id=0ebe3247f844c0e186fd123a2c5fe65207a2fe07
        git remote add ulfh-mmc https://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc.git
        git fetch --no-tags ulfh-mmc next
        git checkout 0ebe3247f844c0e186fd123a2c5fe65207a2fe07
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm olddefconfig
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash dtbs_check