reproduce (this is a W=1 build):
        git checkout a7b10f0963c651a6406d958a5f64b9c5594f84da
        b4 shazam https://lore.kernel.org/r/20251216-b4-ad9467-optional-backend-v1-1-83e61531ef4d@vaisala.com

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-15.1.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=sh olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-15.1.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=sh SHELL=/bin/bash drivers/iio/adc/