reproduce (this is a W=1 build):
        # https://github.com/krzk/linux/commit/1d9addbf90a3a3f0cf5f9629597076d65ac06044
        git remote add krzk-github https://github.com/krzk/linux
        git fetch --no-tags krzk-github b4/mmc-const-sdhci-ops
        git checkout 1d9addbf90a3a3f0cf5f9629597076d65ac06044
        # 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 drivers/mmc/host/