[fpc-pascal] Docs: portability differences between Borland/FPC

[Marco van de Voort]

In our previous episode, Martok said:
> Am 18.08.2018 um 23:25 schrieb Marco van de Voort:
> > Summary: behaviour with range checks off is implementation defined?
> No. "implementation different", but not really "implementation defined".
 
> TP and Delphi are fully defined without range checks. In fact, TP is defined as
> *having no runtime range checks at all* (TP7LG, Chapter 21), except for
> Succ/Pred (and Inc/Dec by extension), which explicitly react to $R (TP7LG,
> Chapter 4) . One might imagine:

Well TP has a conservative codegenerator because its simplicity. Delphi is
heavily versioned, and testing all versions using all options is hard.

... and then even you are not certain it is really intended.