[clang] [clang] Match -isysroot behaviour with system compiler on Darwin (PR #80524)

[Liviu Ionescu via cfe-commits]

ilg-ul wrote:

> they change the behaviour you introduced in https://github.com/llvm/llvm-project/pull/70817 when -isysroot is provided.

I need to take a closer look, since at first reading I can't evaluate the consequences, especially if this does change the behaviour when -isysroot is **not** provided.

And I do not know exactly the use case you are considering. My use case was relatively straightforward, multiple versions of the toolchain are installed in versioned custom folders in user home, and different projects requiring different toolchain versions have symbolic links from the project folder to one of the clang executable.

If your change does not affect the above use case and also adds more consistency with Apple clang, it should be fine.


https://github.com/llvm/llvm-project/pull/80524