[clang] [clang][driver] Add \<executable\>/../include/c++/v1 to include path on Darwin (PR #70817)

[Jon Roelofs via cfe-commits]

jroelofs wrote:

> changing the structure of the symlinks is not possible, it is done automatically by a tool.

To be fair: tools can be changed, and in fact you're proposing to change one ;)

But that said, now I see what you're up against.

https://github.com/llvm/llvm-project/pull/70817