Support for Mac OS 10.6.2

Contributed by Small Tree, adopted to newer fio version by me.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/helpers.c b/helpers.c
index f314ebb..9c76d30 100644
--- a/helpers.c
+++ b/helpers.c
@@ -24,3 +24,16 @@
 {
 	return 0;
 }
+
+int __weak clock_gettime(clockid_t clk_id, struct timespec *ts)
+{
+	struct timeval tv;
+	int ret;
+
+	ret = gettimeofday(&tv, NULL);
+
+	ts->ts_sec = tv.tv_sec;
+	ts->ts_nsec = tv.tv_usec * 1000;
+
+	return ret;
+}