By default, when an ANE is added to a Flex/ActionScript mobile project, it lets you know what are the un-supported targets for that ANE( i.e., both iOS and Android on device and current desktop) whichever are applicable. It is the expected behaviour.
So for the above ANE, it doesn't support launching on Mac Desktop(its just an info to the user that if he tries launching on AIR Simulator it will throw an error if this ANE is added/used in the project), it can be used in the project and can be launched both on iDevice and android device.
Unfortunately you cannot use the iOS simulator in the latest XCode build. This is a bit of a catch-22.
I wonder if this Adobe Blog post could be updated for Desktop Mac: http://www.adobe.com/devnet/air/native-extensions-for-air/extensions/gyroscope.html
Or update the ANE to support desktop. Otherwise, we will get errors like this when we try to use it:
Error occurred while packaging the application:
Error: libgyroscopeExtension.a are required to have universal iOS libraries. Please contact the ANE developer(s) to get the same.