reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git/commit/?id=e7f0b27fbbf1115d93bd108f00ebe7a0428e7e38
        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/kbuild-error-propagation
        git checkout e7f0b27fbbf1115d93bd108f00ebe7a0428e7e38
        # 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