[clang] [clang-format] Add null-terminated path option (#123921) (PR #123926)

[Owen Pan via cfe-commits]

owenca wrote:

> > From #123921, it seems that you only want the new option to work with `--staged`, but should it also work with other options that may print a list of filenames?
> 
> I don't know; I only use `git clang-format` as in #123921 and I am not familiar with all its uses. I was hoping that you or someone other who is familiar could determine this.
> 
> What worries me is conditions where more than one list of files is printed, e.g. unchanged + changed files. It's difficult to parse these messages from the shell; when a null-separated list is printed from other command line utilities, it has one meaning, e.g. "here's the list of files you asked for", whereas `git clang-format` prints other diagnostics too.
> 
> If someone is familiar with the usages of this tool maybe they can tell me what is the logic that must be followed in terms of **which list** is the important one according to the options passed, so that only that list is printed with `--print0`.

It seems that `git-clang-format` was not designed for its output to be consumed by another utility as it prints everything to `stdout` instead of `stderr`. Adding an option like`--print0` (especially just for `--staged`) looks odd to me.

https://github.com/llvm/llvm-project/pull/123926