[clang] [Clang][Driver] Improve config file handling on Darwin (PR #111306)

[Carlo Cabrera via cfe-commits]

carlocab wrote:

> ⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo. Please turn off [Keep my email addresses private](https://github.com/settings/emails) setting in your account. See [LLVM Discourse](https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it) for more information.

This seems to be based on the commit author rather than my actual GitHub configuration. See also https://github.com/llvm/llvm-project/pull/110962#issuecomment-2392834897

https://github.com/llvm/llvm-project/pull/111306