I cannot build and test on devices because Xcode gives me this error:
ld: file is universal (3 slices) but does not contain a(n) armv7s slice: /.../Classes/AddThis/libAddThis.a for architecture armv7s
How do I update this library to support armv7s?
libAddThis.a needs to be built for the armv7s architecture. If you don’t have control over this then you will need to remove armv7s from valid architectures as you did.