runtime: restore nacl timens
Deleted in cl/123700044.
I am not sure whether I need to restore it,
or delete rest of the uses...

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/129580043
diff --git a/src/pkg/runtime/time.go b/src/pkg/runtime/time.go
index 97092c6..c9df3a3 100644
--- a/src/pkg/runtime/time.go
+++ b/src/pkg/runtime/time.go
@@ -34,6 +34,9 @@
 	t            []*timer
 }
 
+// nacl fake time support.
+var timens int64
+
 // Package time APIs.
 // Godoc uses the comments in package time, not these.