anchor.diff:    static String getTag(String mode) {
       if (mode.endsWith('debug-ia32')) return 'DebugIA32';
       if (mode.endsWith('debug-x64')) return 'DebugX64';
  +    if (mode.endsWith('debug-x64c')) return 'DebugX64C';
       if (mode.endsWith('debug-arm32')) return 'DebugSIMARM';
       if (mode.endsWith('debug-arm64')) return 'DebugSIMARM64';
  +    if (mode.endsWith('debug-arm64c')) return 'DebugSIMARM64C';
       if (mode.endsWith('ia32')) return 'ReleaseIA32';
       if (mode.endsWith('x64')) return 'ReleaseX64';
  +    if (mode.endsWith('x64c')) return 'ReleaseX64C';
       if (mode.endsWith('arm32')) return 'ReleaseSIMARM';
       if (mode.endsWith('arm64')) return 'ReleaseSIMARM64';
  +    if (mode.endsWith('arm64c')) return 'ReleaseSIMARM64C';
       throw ('unknown tag in mode: $mode');
     }
   
  
positive.code:   static const List<String> clusterModes = [
      'jit-debug-ia32',
      'jit-debug-x64',
      'jit-debug-arm32',
      'jit-debug-arm64',
      'jit-ia32',
      'jit-x64',
      'jit-arm32',
      'jit-arm64',
      'aot-debug-x64',
      'aot-x64',
    ];
  
    // Modes not used on cluster runs because they have outstanding issues.
  
negative.code:     // Times out often:
      'aot-debug-arm32',
      'aot-debug-arm64',
      'aot-debug-arm64c',
      'aot-arm32',
      'aot-arm64',
      'aot-arm64c',
      // Too many divergences (due to arithmetic):
      'js-x64',
    ];
  