[clang] [clang][Darwin] Remove legacy framework search path logic in the frontend (PR #75841)

[Louis Dionne via cfe-commits]

ldionne wrote:

@jlebar The CI seems to be failing due to a test you were the last to touch:

```
******************** TEST 'Clang :: Preprocessor/cuda-macos-includes.cu' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
[...]
error: CHECK-DAG: expected string not found in input
// CHECK-DAG: ignoring nonexistent directory "/var/empty/System/Library/Frameworks"
              ^
<stdin>:1:1: note: scanning from here
```

Long story short, that test was checking for the diagnostic output from the Frontend complaining that we can't find `/var/empty/System/Library/Frameworks` as a way to ensure that it would normally try searching in those paths for frameworks. This isn't the case anymore since the frontend doesn't know anything about these search paths, and the driver handles them instead.

This shouldn't be a problem if the normal linker is being used when linking object files produced for cuda targets, since the linker on Apple platforms nowadays knows about these search paths, and Clang doesn't really need to specify them explicitly. If that's the case, the test could simply be removed. But I don't know much about cuda, so I'd rather ask in case that's not the case.

https://github.com/llvm/llvm-project/pull/75841