xctool: fix "No architectures to compile for"

When running an xctool action you can face this error:

No architectures to compile for (ONLY_ACTIVE_ARCH=YES, active arch=x86_64, VALID_ARCHS=armv7 armv7s).

The solution is easy, if you know where to look. Go to Project > Build Settings > Architectures > Build Active Architecture Only and set the value to NO.

Piece of cake!

Source