BUG/MEDIUM: threads: don't try to free build option message on exit

Commit 0493149 ("MINOR: thread: report multi-thread support in haproxy -vv")
added information about thread support in haproxy -vv output but accidently
marked the message as "must_free" while it's a constant. This causes a segv
on the old process on clean exit if threads are enabled. It doesn't affect
the stability during operations however.
diff --git a/src/hathreads.c b/src/hathreads.c
index 0db48c9..36bdca2 100644
--- a/src/hathreads.c
+++ b/src/hathreads.c
@@ -155,7 +155,7 @@
 #if defined(DEBUG_THREAD) || defined(DEBUG_FULL)
 	memset(lock_stats, 0, sizeof(lock_stats));
 #endif
-	hap_register_build_opts("Built with multi-threading support.", 1);
+	hap_register_build_opts("Built with multi-threading support.", 0);
 }
 
 #endif