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/bigeasy/staging.git/commit/?id=ebfd80a39c4e2258942c2949863b316607d4700a
        git remote add bigeasy-staging https://git.kernel.org/pub/scm/linux/kernel/git/bigeasy/staging.git
        git fetch --no-tags bigeasy-staging futex_percpu_ref
        git checkout ebfd80a39c4e2258942c2949863b316607d4700a
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=x86_64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/