clang-format: Preserve trailing-comma logic even with comments.

Before:
  vector<int> SomeVector = {// aaa
                            1, 2,
  };

After:
  vector<int> SomeVector = {
      // aaa
      1, 2,
  };

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221699 91177308-0d34-0410-b5e6-96231b3b80d8