enable epoll/ipc on Windows wheels

[minrk]

Initially enabled in #1570, epoll has been disabled in our wheels due to causing unavoidable crashes for some users (#1981, #1754, #1999)

Because these crashes are relatively rare, users installing pyzmq from source can still enable it, and pyzmq will follow libzmq's own defaults and build with epoll/ipc enabled:

pip install --no-binary pyzmq pyzmq

We should not re-enable ipc in our Windows wheels until there is a confirmed fix for zeromq/libzmq#4730 (it is incredibly hard to test)

[ToucanBran]

any updates on re-enabling IPC on the windows wheels? I'd really like to use ipc

[minrk]

We need to wait for a libzmq release where ipc doesn't cause crashes on Windows.