reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/commit/?id=54d41ebbde875a89d5f61fa3fb26291ece399fb2
        git remote add ebiggers https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git
        git fetch --no-tags ebiggers sha256-lib-cleanup-v2
        git checkout 54d41ebbde875a89d5f61fa3fb26291ece399fb2
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-15.1.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-15.1.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash lib/crypto/