[fpc-pascal] Get variable name at runtime

[Marco van de Voort]

In our previous episode, Mark Morgan Lloyd said:
> I meant that in the context of FPC, which works out dependencies etc. on 
> the fly, one can't arbitrarily hook in an external preprocessor. I meant 
> that it wasn't another stage in a makefile because FPC doesn't (can't) 
> use makefiles- for reasons that you explained yesterday.

That's technically impossible, since how the preprocessor influences
dependencies is not know to the compiler.

It is the same discussion as the make -j bit. If you want a C compiling
model, don't use units and use {$i} and manually link it together, like in C.

I prefer the unit model though.