Compilation error `invalid pragma: stackTrace: off`

```nim
import chronos

proc callProc[T](f: proc (): T): T =
  f()

proc foo() {.async.} =
  callProc do {.async.}:
    discard
```
Compiled with `nim c -d:asyncBackend=chronos`

nim: 2.0.8
chronos: 4.0.2

The same code works with asyncdispatch.