Compile issues on MacOSX

[job]

There seem to be at least 2 problems:

MacOSX doesn't seem to have SOCK_CLOEXEC, so perhaps #define SOCK_CLOEXEC FD_CLOEXEC in a header is useful?

Also, MacOSX doesn't have ppoll(), so probably should use poll() instead? Is &oldmask critical in proc_rsync()?

[job]

Does this approach perhaps work? https://github.com/ArduPilot/ardupilot/pull/8593/files

[kristapsdz]

CLOEXEC is the easy part: it's the ppoll(2) that's the hard part. I'll need to do this on NetBSD as well---I'll get around to it!