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

[Liviu Ionescu via cfe-commits]

ilg-ul wrote:

After several more attempts I identified the reason for the failure: the folder structure in the build location does not include the `bin/../include/c++/v1` folder required for this to work:

```
clang version 18.0.0 (https://github.com/llvm-premerge-tests/llvm-project.git 6bfa3255358eeb2b109525059920e5f2b2abe41b)
Target: x86_64-apple-darwin
Thread model: posix
InstalledDir: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-tdgkv-1/llvm-project/clang-ci/build/build-clang/tools/clang/test/Driver/Output/darwin-header-search-libcxx.cpp.tmp/xpacks/.bin
ignoring nonexistent directory "/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-tdgkv-1/llvm-project/clang-ci/build/build-clang/tools/clang/test/Driver/Output/darwin-header-search-libcxx.cpp.tmp/xpacks/.bin/../include/c++/v1"
ignoring nonexistent directory "/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-tdgkv-1/llvm-project/clang-ci/build/build-clang/bin/../include/c++/v1"
```

After creating this include folder, the Linux test finally passed.

I don't know if creating this folder is acceptable for the testing infrastructure, but if we want this test together with the bug fix, we probably have no other choice.

Louis @ldionne, could you review the test code?




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