only compile coro.nim by avoiding "when isMainModule" string match in

testament/tester

FAIL: coro.nim
Test "lib/pure/coro.nim" in category "lib"
Failure: reOutputsDiffer
Expected:

Gotten:
c1
c2
c2
c1
c2
c1
c2
c1
c1 exits
c2 exits
done 1100220033

lib/pure/coro.nim

@@ -119,7 +119,7 @@ proc wait*(c: proc(), interval=0.01) =
   while alive(c):
     suspend interval
 
-when isMainModule:
+when defined(nimCoroutines) and isMainModule:
   var stackCheckValue = 1100220033
   proc c2()