This keeps the size of the fcserver binary down.

This was causing deadlocks all over on Windows. Now things seem to be
running smoothly!

This is necessary for URBs which synchronously complete. This is common on
the win32 backend.

The hotplug branch in manuelnaranjo's repo has very broken support for
composite devices, blah. So let's switch back to libusbx master and deal
with that.