Undefined symbols for architecture armv7: "_OBJC_CLASS_$_GGLContext", referenced from: objc-class-ref in AppDelegate.o
"The OPN [Debug] target overrides the OTHER_LDFLAGS build setting". This was the main issue. After adding $(inherited) in new line in other linker flags solved my issue.
if you are using pod to install the libraries like the link suggests, make sure you check whether there are any errors when you run pod install. It could be that you have changed the OTHER_CFLAGS or OTHER_LDFLAGS in the build settings, that could lead to problem.If that's the case you probably want to add "$(inherited)" in a new line to both those flags.