I'm using an older version of XCode and haven't bothered looking at how the interface might have changed in the newer versions, but this is generally solved for me by modifying the User Search Paths under your project settings. Look at the screenshot, add /usr/local/include
to Header Search Paths and make Always Search User Paths "Yes." That should do the trick
Edit:
One more thing to note, this is only /usr/local/include
because that's the default install directory for the portaudio.h file in the portaudio build (as it is with many libraries).
If you have a different prefix other than /usr/local/include
, add that instead.