reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/commit/?id=7b4af8522254f58e9c812362d173b7417a7cc3da
        git remote add leon-rdma https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git
        git fetch --no-tags leon-rdma dmabuf-vfio
        git checkout 7b4af8522254f58e9c812362d173b7417a7cc3da
        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=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash