clang-format: Prevent ObjC code from confusing the braced-init detection

This was leading to bad formatting, e.g.:
Before:
  f(^{
      @autoreleasepool {
        if (a) {
          g();
  }
  }
  });

After:
  f(^{
      @autoreleasepool {
        if (a) {
          g();
        }
      }
  });