You can do it easier.
Go to your Proejct, go to your target, then "Build Phases" Tab, then to the Compile Sources ->
Find the code files of the library you are trying. and double click on it, you will be able to insert compiler flags.
Type in here
If you add that, it won't try to do ARC compiling on these files
🙂
Or you can just convert the files to ARC with the build in ARC-Converter ;p