Repository: flutter
Issue: Cannot build and run app after updating to Xcode 12 (iOS 14): Target debug_universal_framework failed: Exception: Unsupported iOS arch name
Labels: c: crash,tool,t: xcode,P2,team-tool,triaged-tool

<!-- Thank you for using Flutter!

     If you are looking for support, please check out our documentation
     or consider asking a question on Stack Overflow:
      * https://flutter.dev/
      * https://api.flutter.dev/
      * https://stackoverflow.com/questions/tagged/flutter?sort=frequent

     If you have found a bug or if our documentation doesn't have an answer
     to what you're looking for, then fill out the template below. Please read
     our guide to filing a bug first: https://flutter.dev/docs/resources/bug-reports
-->

## Steps to Reproduce

<!-- You must include full steps to reproduce so that we can reproduce the problem. -->

Before updating yesterday to Xcode 12, everything was running perfectly. When I updated to the newest version of Xcode my iOS app won't build or run on physical device and simulator. Xcode build ends with an error saying "module cloud_firestore not found". I'm using Runner.xcworkspace and I already updated cloud_firestore to the latest version. However every module of my application has this problem (even deleting the import of cloud_firestore, the build ends with another "module xxx not found". 
This is the output of flutter doctor -v:

```
[✓] Flutter (Channel dev, 1.22.0-12.0.pre, on Mac OS X 10.15.4 19E287, locale
    it-IT)
    • Flutter version 1.22.0-12.0.pre at /Users/tiziano/Desktop/Sviluppo/flutter
    • Framework revision a27c242b0e (6 giorni fa), 2020-09-11 17:46:57 -0400
    • Engine revision fee6f9e533
    • Dart version 2.10.0 (build 2.10.0-110.0.dev)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tiziano/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.0, Build version 12A7209
    • CocoaPods version 1.9.3

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 48.1.2
    • Dart plugin version 193.7361
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.49.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.14.1

[✓] Connected device (2 available)
    • AUM L29 (mobile)  • QDG9X18827W03119                     • android-arm64 •
      Android 8.0.0 (API 26)
    • iPhone 8 (mobile) • 702B0408-7B1E-4176-BCD3-89500F520FE7 • ios           •
      com.apple.CoreSimulator.SimRuntime.iOS-14-0 (simulator)

• No issues found!
```

This is the output from flutter run --verbose:
[Terminal Output.txt](https://github.com/flutter/flutter/files/5244668/Terminal.Output.txt)

This is the output from Xcode:
![Schermata 2020-09-18 alle 11 18 44](https://user-images.githubusercontent.com/36270604/93581116-fc3a8a80-f9a0-11ea-8b3f-75fe3cb21766.png)

I also tried deleting Podfile, Pods, and then pod install, still didn't work. I Also tried pod deintegrate and then pod install, didn't work neither. I also tried to switch from stable channel to dev channel, still didn't work.