Add header <atomic> which is needed to compile with some older library versions.
// RUN: XRAY_OPTIONS="verbosity=1" %run %t
// RUN: rm xray-log.fdr-reinit* || true
#include "xray/xray_log_interface.h"
+#include <atomic>
#include <cassert>
#include <cstddef>
#include <thread>
