After downloading Xcode 6 beta 6, If you are receiving Apple Mach-O Linker error, Undefined symbols for architecture then try clearing the DerivedData for Xcode.
Undefined symbols for architecture x86_64:
“__TFSs26_forceBridgeFromObjectiveCU__FTPSs9AnyObject_MQ__Q_”, referenced from:
Derived data folder location
You find out the location of derived data using Xcode Preferences. Click Xcode -> Preferences.
Click Locations tab and navigate to Derived Data section. Then click the arrow next to folder the path.
Now delete DerivedData folder under Xcode.