[clang-format] Add ability for clang-format-diff to exit with non-0 status (#70883)

This patch adds the ability for the clang-format-diff script to exit
with a non-zero status if it detects that formatting changes are
necessary. This makes it easier to use clang-format-diff as part of a
DevOps pipeline, since you could add a stage to run clang-format-diff
and fail if the formatting needs to be fixed.