[clang] [clang][driver] Prevent clang picking the system headers when started via a symlink (PR #68091)

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nolange wrote:

> @nolange, English is not my first language, and I know sometimes I'm very confusing. In my understanding, the title suggest that if clang is not invoked directly but via a symlink, it does not behave correctly, i.e. instead of picking the headers from the folders where clang is installed, it picks the system headers. This is documented with examples in the bug report.

Yes, my problem with the title is, that it sound like you want to change the way how clang should behave when using symlinks.

> 
> If this is not what the title reads, please suggest a better phrasing.

Here is how I would phrase it:
"Fix an issue where clang does not correctly resolve the system header if invoked via symlink" (on MacOS)

Main point being that you fix a bug and don't want to change the usual behavior (like gcc, like it works on Linux),
and that you don't **prevent** clang picking up the system headers but **fix** picking up the system headers .
This is how I understand the Bug Report and the discussion.

https://github.com/llvm/llvm-project/pull/68091