[fpc-pascal] Large file support

[Marco van de Voort]

In our previous episode, Mark Morgan Lloyd said:
> 
> 8 apparently, but off_t is documented as a cint32.
> 
> https://www.freepascal.org/docs-html/current/rtl/unixtype/off_t.html

The declaration is 

{$if not defined(fs32bit)}
    off_t    = cint64;          { used for file sizes          }
{$else}
    off_t    = cint;
{$endif}

The 64bit is active, IIRC the 32-bit is for use with FPC_USE_LIBC for when
the debian oldstable still defined 32-bit as seek (even though even somewhat
relevant distros already defined 64-bit).  

FPC_USE_LIBC for linux and *bsd still is still hardly used afaik.

Maybe we could clean it out. Why the documentation tool picks the $ELSE
branch I don't know. I grepped, and it didn't seem to find anything in fpdoc
or (doc/rtl) makefiles defining it.