Go to > Definition(s) Question/Issue

In a C file, if I right click a function call I can navigate the context menu to "Go To" > "Definition" or "Definition(s)" to go to its definition. However, I am having issues when there are multiple definitions/implementations in different files. Each file has a different implementation based on platform, and only one file is actually included in the project depending on context/platform. I would expect "Go To" > "Definition" to go to the correct file for the current context/platform, however, CLion is choosing a file that's not even included in the project at all (I can tell, because in the Project View the file name is grayed out). I thought that "Go To" > "Definition(s)" might list all the files the definitions are in and allow me to chose which one, however, it does the same thing as "Go To" > "Definition". 

What am I missing here? How do I navigate to the appropriate function definition/implementation?