reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=ebbbb0910e2fb82b773ba3b0ced0f843eed79436
        git remote add ardb https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git
        git fetch --no-tags ardb la57-cpucap-v4
        git checkout ebbbb0910e2fb82b773ba3b0ced0f843eed79436
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash