DLL specific defines

[Patrik Stridvall]

> > With the patch below this is added as EXTRADEFS
> > flags so I can pick it up from the Makefile_in's
> > and convert to .dsp compile rules.
> wouldn't it be better to add them to another specific define
> (like EXTRAWINDEFS or something) just to really know what
> they are for ?

If you wish. I don't care either way.

I just want the defines somewhere so I can find them
in the Makefile.in to .dsp/.dsw convertor.