text: Title: On the clang-format check of the project
  Body: I noticed that horovod use [clang-format](https://clang.llvm.org/docs/ClangFormat.html) to format C++ code.
  
  But when I check the project with clang-format-12, I still got many errors. The cmd I used as below:
  ```bash
  #!/usr/bin/env bash
  
  for src in $(find ./horovod -name "*.h" -or -name "*.cc")
  do
   clang-format-12 -style=file ${src}
  done
  ```
  
  And the output as attached [hvd_cf12.txt](https://github.com/horovod/horovod/files/8220236/hvd_cf12.txt).
  
  May I know did I use the wrong clang-format version, or the cmd is not right?
  