Xcode 6 linker error - Undefined symbols for architecture armv7

Question

After upgrading to Xcode 6 beta 7 (and now still with Xcode 6 GM) I am unable to link my Swift app. I receive errors such as:

Undefined symbols for archit

Answer 1

I have solved my issue by deleting all the data in the ~/Library/Developer/Xcode/DerivedData folder. I read about that in another thread, but ignored it thinking a clean included that process!