Add "clang-format-on-save-mode" minor mode to clang-format.el (#104533)
Add an minor mode which can be optionally used to run clang-format on
save.
Formatting before saving works well and is convenient to avoid having to
remember to manually run clang format.
I've written this as it's own package but it's probably better if the
functionality is supported by clang-format.el.
See: https://github.com/melpa/melpa/pull/8762