reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=99ece3600fdb60fef87268c6c05c66e5d02dbeb4
        git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
        git fetch --no-tags linux-next master
        git checkout 99ece3600fdb60fef87268c6c05c66e5d02dbeb4

        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=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash drivers/gpu/drm/amd/amdgpu/