Can you say a little more about the problem you're trying to solve? E.g., do you want to conditionally include ipp.h or a different .h file depending on whether the switch is used? Or conditionally call one function or another depending on the presence or absence of ipp? This will help us understand if there's a better solution or make a case for adding something in the compiler to help you.
The reason is exactly as you say: "Conditionally call one function (or include a header file) or another depending on the presence or absence of ipp". I am dealing with code that has to run on different architectures. On some of them, the IPP might not be available. So I have to have code that uses the IPP and code that can work around this (by using different libraries).
I agree that I can use a define that I create myself to select the code branches. I just wondered if there is already such a define which I could use.
So, I do not think that it is critical to me to have such a define. It would be nice though :-)