asyncdispatch: fix erroneous set construction (#13765)
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.
dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim,dom96/Nim