[fpc-pascal] detect the version of fpc that a feature added to it

[Marco van de Voort]

In our previous episode, ik said:
> I was looking to understand in what version of FPC ($IF defined ... } was
> added, and realized that it is not very simple to detect such information.

True. SVN logs of documentation and compiler is the easiest. But that can be
exhausting. 

But $if is old. Wouldn't be surprised if the 2.x series all supported it.

In general I usually define the oldest version I want to support (now 2.4.4,
but from experience 2.4.2 usually works too), and dl and test with that
version (and intermediate ones).

Daniel: this is a language feature, the bugreport is about the same problem
for libraries.