reproduce (this is a W=1 build):
        # https://github.com/litex-hub/linux/commit/a660177ff3fbae37ae7f2537ff1605956d930e7d
        git remote add litex-hub https://github.com/litex-hub/linux
        git fetch --no-tags litex-hub litex-rebase
        git checkout a660177ff3fbae37ae7f2537ff1605956d930e7d

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # apt-get install sparse
        # sparse version: v0.6.4-73-gfbdde312

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=alpha olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=alpha SHELL=/bin/bash drivers/block/ drivers/fpga/ drivers/gpio/