reproduce (this is a W=1 build):
        git remote add shuah-kselftest https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git
        git fetch shuah-kselftest next
        git checkout shuah-kselftest/next
        b4 shazam https://lore.kernel.org/r/ab29J6KsQm8Xg3LR@NH27D9T0LF
        # apt-get install llvm-dev

        # save the config file
        make W=1 ARCH=i386 olddefconfig
        make W=1 ARCH=i386 
        make W=1 headers_install
        make W=1 -C tools/testing/selftests