GCC doesn't have built in macros for those either, you have to define them in the project file. Certain IDEs will automatically define those for you when it creates the project. I'm pretty sure XCode does, which is what I assume you were using by the __powerpc__ macro. I think the Visual C++ argument is the same as GCC -D __x86_64__
Are you sure about that? I always thought that definitions beginning with a double underscore (__mips__ / __alpha__ / __powerpc__ etc) were somehow predetermined by the compiler. In fact I'm pretty sure they are, although I don't know how.
"A problem well stated is a problem half solved.” - Charles F. Kettering
Huh, I guess I was wrong, it is predetermined by the compiler. But it's not standard, it's predetermined by the GCC compiler. GCC does this, MinGW doesn't (I just tested it), so I would assume VC++ doesn't either. It shouldn't be hard to define though in your project. I'm not sure where you define the global definitions, but I know there is a way to do it.