Replace wait channel polling with simple sleep for portability.

Fix timeouts in poll/select regress tests

Disable poll/select timeout so that the wchan wait would work as
intended. The timeout is not essential to the test flow. In addition,
the top-level alarm t

Fix timeouts in poll/select regress tests

Disable poll/select timeout so that the wchan wait would work as
intended. The timeout is not essential to the test flow. In addition,
the top-level alarm timer prevents the tests from getting stuck should
something go wrong.

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Add tests for concurrent closing of a poll/select monitored fd.