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

This seems to be caused (for most) by linking a third-party library that does not support the requested architecture.