we already have an option for this    https://github.com/ceph/ceph/blob/c1112928b7926fdc0a53d254a5f72055728f3b58/CMakeLists.txt#L572    which sets     https://github.com/ceph/ceph/blob/c1112928b7926fdc0a53d254a5f72055728f3b58/src/include/config-h.in.cmake#L280-L281