made some tests green

tests/threads/tthreadanalysis.nim

@@ -1,5 +1,7 @@
 discard """
   outputsub: "101"
+  msg: "Warning: write to foreign heap"
+  line: 37
   cmd: "nimrod cc --hints:on --threads:on $# $#"
 """
 
@@ -8,7 +10,7 @@ import os
 var
   thr: array [0..5, TThread[tuple[a, b: int]]]
 
-proc doNothing() = nil
+proc doNothing() = discard
 
 type
   PNode = ref TNode