Preserve timestamps for unchanged files. (#2568)
Preserve timestamps for unchanged files. (#2568)

* Preserve timestamps for unchanged files.

Adding `IncludeBlocks: Merge` apparently triggers a bug in
clang-format(1), where it changes the timestamp of the file even if
there are no formatting changes. I think we want that directive, so I
changed the check-style.sh script to workaround the issue.

While testing this I discovered that cmake-format has the same problem,
so I worked around that bug too.

Finally, I made some cosmetic changes to make my IDE happy inside this
script.

* Address review comments.

* Address review comments.

googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp