improvements to get code size down for programs that don't use GC

tests/stckovfl.nim

@@ -1,7 +1,9 @@
 # To test stack overflow message
 
 proc over(a: int): int = 
-  if a == high(int): return
+  if a >= 400:
+    assert false
+    return
   result = over(a+1)+5
   
 Echo($over(0))