reproduce (this is a W=1 build):
        # https://github.com/jpirko/linux_mlxsw/commit/1c79063b436b437afd074eb39f2374b27ac91aa2
        git remote add jpirko-mlxsw https://github.com/jpirko/linux_mlxsw
        git fetch --no-tags jpirko-mlxsw combined_queue
        git checkout 1c79063b436b437afd074eb39f2374b27ac91aa2

        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=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=nios2 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/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=nios2 SHELL=/bin/bash drivers/mailbox/ drivers/tty/serial/