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.

mercurial/debugcommands.py

@@ -2818,11 +2818,16 b' def debugwireproto(ui, repo, **opts):'
         elif action == 'close':
             peer.close()
         elif action == 'readavailable':
-            fds = util.poll([stdout.fileno(), stderr.fileno()])
-
-            if stdout.fileno() in fds:
+            fds = [stdout.fileno(), stderr.fileno()]
+            try:
+                act = util.poll(fds)
+            except NotImplementedError:
+                # non supported yet case, assume all have data.
+                act = fds
+
+            if stdout.fileno() in act:
                 util.readpipe(stdout)
-            if stderr.fileno() in fds:
+            if stderr.fileno() in act:
                 util.readpipe(stderr)
         elif action == 'readline':
             stdout.readline()