title: Crash on dyld: Library not loaded: /usr/lib/swift/libswift_Concurrency.dylib running on simulator
body: <p>I'm implementing a very basic task (download few files from a remote server) on an existing app, to exercise the new Swift Concurrency APIs. The task is done flawlessly on iOS 15: I use a TaskGroup and I receive the images as expected.
  As this app already exists, I used the @available tag to check if the device can perform my task (if iOS 15, do it. Otherwise, show an alert to the user and do nothing)
  The problem happens when I try to run this app on a simulator with iOS 13.5, my app crash upon the start with the following error:</p>
  <pre><code>dyld: Library not loaded: /usr/lib/swift/libswift_Concurrency.dylib
    Referenced from: /Users/username/Library/Developer/CoreSimulator/Devices/B316A0F0-B7EF-4F5E-8A26-F7FF54E8A681/data/Containers/Bundle/Application/6CF3D46E-3F15-4FA3-BD61-9D353541B9DA/MyApp.app/MyApp
    Reason: image not found
  dyld: launch, loading dependent libraries
  DYLD_SHARED_CACHE_DIR=/Users/username/Library/Developer/CoreSimulator/Caches/dyld/20F71/com.apple.CoreSimulator.SimRuntime.iOS-13-5.17F61
  DYLD_ROOT_PATH=/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 13.5.simruntime/Contents/Resources/RuntimeRoot
  DYLD_LIBRARY_PATH=/Users/username/Library/Developer/Xcode/DerivedData/MyApp-bawyiebpygwuwxawcoistefwxuyy/Build/Products/Debug-iphonesimulator:/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 13.5.simruntime/Contents/Resources/RuntimeRoot/usr/lib/system/introspection
  DYLD_INSERT_LIBRARIES=/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 13.5.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libBacktraceRecording.dylib:/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 13.5.simruntime/Contents/Resources/RuntimeRoot/usr/lib/libMainThreadChecker.dylib:/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 13.5.simruntime/Contents/Resources/RuntimeRoot/Developer/Library/PrivateFrameworks/DTDDI
  </code></pre>
  <p>Environment: Xcode 13.0 beta 2 (13A5155e) Simulator iPhone 8 (iOS 13.5). Swift Language Version 5</p>
  <p>Is there something that I can do about it?</p>
  <p><strong>Edit:</strong> this is how I'm using the if available</p>
  <pre><code>@available(iOS 15.0, *)
  class SCTestViewController: UIViewController {...}
      
  </code></pre>