asyncdispatch: fix erroneous set construction (#13765)

These constants were defined as `cint`. They can be huge on certain
systems, such as Haiku, and trigger out-of-bounds errors in
asyncdispatch.

Ref #13764.

lib/pure/asyncdispatch.nim

@@ -1407,7 +1407,9 @@ else:
                      MSG_NOSIGNAL)
       if res < 0:
         let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
+        if lastError.int32 != EINTR and
+           lastError.int32 != EWOULDBLOCK and
+           lastError.int32 != EAGAIN:
           if flags.isDisconnectionError(lastError):
             retFuture.complete()
           else: