reproduce (this is a W=1 build):
        # https://github.com/kkdwivedi/linux/commit/280ac9dc2846a4a9c68adefea007239b3642d07f
        git remote add kkdwivedi https://github.com/kkdwivedi/linux
        git fetch --no-tags kkdwivedi fermata
        git checkout 280ac9dc2846a4a9c68adefea007239b3642d07f
        # apt-get install sparse
        # sparse: v0.6.5-rc1

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um SHELL=/bin/bash kernel/