Consider removing BROKEN_POLL check
Add cmake check for BROKEN_POLL
I'm not really sure why dbus even has this check - as far as I can see, we're careful to only poll things we can rely on being able to poll, notably not including devices:
- pipes (Unix only)
- inotify (Linux and QNX only)
- kqueue (*BSD only)
I would suggest dropping this commit, and making the CMake build just assume that poll() works. We can consider whether to drop the Autotools check as a separate issue.
This is that separate issue.