xcodebuild clean fails when SwiftPM has been integrated into the app.

1. flutter config --no-enable-swift-package-manager
2. flutter create my_app --platforms ios && cd my_app
3. flutter pub add image_picker
4. flutter build ios
5. xattr -l build/ios
   • Expected & Actual output: nothing
6. xattr -l build/ios/iphoneos
   • Expected & Actual output: nothing
7. xattr -l build/ios/Release-iphoneos
   • Expected & Actual output: com.apple.xcode.CreatedByBuildSystem: true
8. cd ios && xcodebuild clean -scheme Runner -workspace Runner.xcworkspace -configuration Release -sdk iphoneos -destination "generic/platform=iOS" BUILD_DIR="../build/ios"
   • Expected & Actual output: ** CLEAN SUCCEEDED **
   • If you check ls ../build/ios, you will see Release-iphoneos was deleted
9. flutter config --enable-swift-package-manager
10. cd .. && flutter clean
11. flutter build ios
12. xattr -l build/ios
    • Expected output: nothing
    • Actual output: com.apple.xcode.CreatedByBuildSystem: true
13. xattr -l build/ios/iphoneos
    • Expected & Actual output: nothing
14. xattr -l build/ios/Release-iphoneos
    • Expected output: com.apple.xcode.CreatedByBuildSystem: true
    • Actual output: nothing
15. cd ios && xcodebuild clean -scheme Runner -workspace Runner.xcworkspace -configuration Release -sdk iphoneos -destination "generic/platform=iOS" BUILD_DIR="../build/ios"
    • Expected output: ** CLEAN SUCCEEDED **
    • Actual output:

error: Could not delete `/path/to/my_app/build/ios/Release-iphoneos` because it was not created by the build system and it is not a subfolder of derived data.
    note: To mark this directory as deletable by the build system, run `xattr -w com.apple.xcode.CreatedByBuildSystem true /path/to/my_app/build/ios/Release-iphoneos` when it is created.
** CLEAN FAILED **

This is a problem for Flutter because we use clean when engine headers change: