[fpc-pascal] Using platform specific include files like FPC does

[Marco van de Voort]

In our previous episode, Graeme Geldenhuys said:
> How do I use platform specific include files like FPC does, but in my
> own projects?

FPC has actually several schemes.

The most common two are:

1 {$ifdef'ed} inclusion of includefiles.
2 having make set the includedir to a target version.
 
The first is dead simple, the second depends on your makefile system.

Note that afaik the main reason FPC does this is because too many ifdefs
make the source unreadable. It is not because of a grudge against ifdefs.