reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git/commit/?id=01fa4954564be77b8e5affd0825952e0a88d5bca
        git remote add thomas-weissschuh https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git
        git fetch --no-tags thomas-weissschuh b4/vdso-asm-generic-vsyscall-h
        git checkout 01fa4954564be77b8e5affd0825952e0a88d5bca

        # install sparc64 cross compiling tool for clang build
        # apt-get install binutils-sparc64-linux-gnu
        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=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=sparc64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=sparc64 SHELL=/bin/bash