[fpc-pascal] (Unix) serial port handling

[Marco van de Voort]

In our previous episode, Mark Morgan Lloyd said:
> > fsync just makes sure all the in-kernel caches are written to the 
> > device.  Flushing input data is just a matter of reading it.
> 
> Thanks for that Henry. Obviously there's scope for confusion here with 
> the kernel's tcflush() and tcdrain() functions, where tcflush discards 
> input and/or output data.

(For *nix, implementations of that are in unit termio)