MINOR: threads: always place the clockid in the struct thread_info

It will be easier to deal with the internal API to always have it.
diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 0dbec67..6c420dd 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -50,6 +50,7 @@
 enum { tid = 0 };
 
 extern struct thread_info {
+	clockid_t clock_id;
 	/* pad to cache line (64B) */
 	char __pad[0];            /* unused except to check remaining room */
 	char __end[0] __attribute__((aligned(64)));