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

[Martok]

Hi all,

There is the old "Porting TP" document at <https://www.freepascal.org/port.var>, but it is rather incomplete (and probably on an
older language level). It also covers mostly syntactic differences - things a programmer will notice because of the error messages.

Since #34140 was again someone tripping over an obscure difference between what is documented for the Borland compilers and what
is not actually documented in FPC (there's a reason #16006 has so many dupes), I've started writing up some of these things that
I could think of right away on the wiki, for now as a draft under my user namespace:
<http://wiki.freepascal.org/User:Martok/Portability_Issues>

Feel free to suggest more non-obvious topics (or make additions directly, it's a wiki). The general pattern for each topic is
"short summary"-"example"-"contrast"-"links". Include citations if possible, especially for the Borland side of things. FPC is
easy enough to reproduce for everybody.

-- 
Regards,
Martok