.arcconfig

debugwireproto: handle unimplemented util.poll() for Windows

This is the same logic used in sshpeer.doublepipe.  It doesn't completely fix
test-ssh-proto{,-unbundle}.t ("read(-1) -> X" is changed to "read(X) -> X", the
order of some lines are changed, and abort messages seem to be missing), but it
cuts down a ton on the failure spew.

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