[4.1] f6a7903 Mark [u]sleep() to not check return value by default

[Poul-Henning Kamp]

commit f6a7903640ba5b3b91abcecbdbed0aa99766fbd1
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Sat Jul 11 20:13:46 2015 +0000

    Mark [u]sleep() to not check return value by default

diff --git a/flint.lnt b/flint.lnt
index 000968a..434c54a 100644
--- a/flint.lnt
+++ b/flint.lnt
@@ -38,6 +38,9 @@
 -esym(534, strlcpy)
 -esym(534, strncpy)
 
+-esym(534, sleep)
+-esym(534, usleep)
+
 ///////////////////////////////////////////////////////////////////////
 // <vas.h>