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/src/haproxy.c b/src/haproxy.c
index 692c333..1c5898e 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2500,6 +2500,8 @@
 
 #ifdef USE_THREAD
 	pthread_getcpuclockid(pthread_self(), &thread_info[tid].clock_id);
+#else
+	thread_info[tid].clock_id = CLOCK_THREAD_CPUTIME_ID;
 #endif
 
 	tv_update_date(-1,-1);