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

[Louis Dionne via cfe-commits]

================
@@ -2494,6 +2494,19 @@ void DarwinClang::AddClangCXXStdlibIncludeArgs(
                    << "\"\n";
     }
 
+    // Check for the folder where the executable is located, if different.
----------------
ldionne wrote:

```suggestion
    // (2) Check for the folder where the executable is located, if different.
```

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