reproduce (this is a W=1 build):
        # https://github.com/ClangBuiltLinux/linux/commit/532a7ac2d57bb5674f5feffb4ba378f8a32f3bcf
        git remote add clangbuiltlinux https://github.com/ClangBuiltLinux/linux
        git fetch --no-tags clangbuiltlinux question_mark_operator
        git checkout 532a7ac2d57bb5674f5feffb4ba378f8a32f3bcf
        # 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=i386 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=i386 SHELL=/bin/bash drivers/gpu/drm/