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

[Liviu Ionescu via cfe-commits]

ilg-ul 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.

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

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