compiler error on simple async proc
```nim
import pkg/chronos

proc f {.async.} =
  discard

waitFor f()
```

compile error (WSL2 `nimble build`)
```
~/.nimble/pkgs2/chronos-3.2.0-5783067584ac6812eb64b8454ea6f9c97ff1262a/chronos/asyncloop.nim(850, 35) template/generic instantiation of `unregister2` from h
ere
~/.nimble/pkgs2/chronos-3.2.0-5783067584ac6812eb64b8454ea6f9c97ff1262a/chronos/ioselects/ioselectors_epoll.nim(459, 22) Error: attempting to call undeclared
 routine: 'none'
```
compile error (WSL2 `nimble build -d:mingw`)
```
# WSL2 nimble build -d:mingw
/home/doongjohn/.nimble/pkgs2/chronos-3.2.0-5783067584ac6812eb64b8454ea6f9c97ff1262a/chronos/asyncloop.nim(1286, 12) Error: attempting to call undeclared routine: 'some'
```

nim version:
```
Nim Compiler Version 1.9.5 [Linux: amd64]
Compiled at 2023-07-28
Copyright (c) 2006-2023 by Andreas Rumpf

git hash: f1ac979184ad7fa0d8c44415e781181a00a0095f
active boot switches: -d:release
```