Use nanosleep in Linux sched_yield(2) workaround

CHANGES

@@ -6,6 +6,7 @@ OpenLDAP 2.3.17 Engineering
 	Fixed slapd-ldap idassert anon2anon issue (ITS#4321)
 	Fixed slapd-monitor thread issue (ITS#4318)
 	Build environment
+		Updated Linux sched_yield(2) workaround to use nanosleep(2) (ITS#3950)
 		Fixed configure report-to URL
 
 OpenLDAP 2.3.16 Release

configure.in

@@ -1589,6 +1589,7 @@ dnl			[ol_cv_pthread_lpthread_lexc])
 			ol_replace_broken_yield=no
 			case "$target" in
 			*-*-linux*) 
+				AC_CHECK_FUNCS(nanosleep)
 				ol_replace_broken_yield=yes
 			;;
 			esac