<incomplete type> is the error that results when "something has gone wrong and gdb can't figure out what the type of variable x is". There are many possible causes, and there's unlikely to be one workaround.
One common cause is that you turned on "dead code stripping" but not -gfull. That can cause corruption in the debug info.
I actually can't tell from the build settings below whether this is the case. I think you need to cut & paste them from the target not the project? Anyway, if GCC_DEBUGGING_SYMBOLS really were "", then you wouldn't get as far as <incomplete type> so those can't be the whole story...
Anyway, if you can file a bug on it, that would be really helpful. I have no way to tell what's going on or fix it without more information.... To analyze the problem I need to get my hands on a debug version of your project, the XCode-gdb transcript of a run that got you to the point where you saw the <incomplete type> error, and instructions on what I had to do with your app to get it to that point.
I don't need sources or the Xcode project, just the debug executable/framework/whatever... If your company is okay with making that available, then please do file a bug with the information mentioned above, and I will look into it.
Jim