reproduce (this is a W=1 build):
        # https://github.com/frank-w/BPI-R2-4.14/commit/4acdbb18ee854e8d5ff467e474421cece28c3d23
        git remote add frank-w-bpi-r2-4.14 https://github.com/frank-w/BPI-R2-4.14
        git fetch --no-tags frank-w-bpi-r2-4.14 6.18-rc
        git checkout 4acdbb18ee854e8d5ff467e474421cece28c3d23
        # install powerpc cross compiling tool for clang build
        # apt-get install binutils-powerpc-linux-gnu
        # clang-22 might not be officially released. Try a lower version if installation fails.
        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=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash drivers/clk/mediatek/