Solved thanks to @shazron
Add this line to your Build Settings -> Header Search Paths:
"$(OBJROOT)/UninstalledProducts/$(PLATFORM_NAME)/include"
Don't replace the existing line that looks similar, that is still needed to be backwards compatible with Xcode 7 and Xcode 6.4.
This probably had something to do with tvOS, I reckon -- Apple had to separate the archive intermediates by platform for universal builds.