For some future person Googling (or who knows, maybe in the future we'll all be Binging, or hopefully Burfording).
I wanted a project using a new library that uses ARC to still work on older iOS 4 devices. Even adding the -fobjc-arc flag to the other linker flags didn't help.
dyld: lazy symbol binding failed: Symbol not found: _objc_retain
In the end I also added to the Other Linker Flags: -weak_library /usr/lib/libobjc.A.dylib
That DID work to get it running without errors. Probably could add that other ways, but it worked...