[clang-tools-extra] [clang-include-cleaner] Fix incorrect directory issue for writing files (PR #111375)

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet requested changes to this pull request.

thanks a lot for the patch, and sorry for regressing this.

I think this is also going to regress behavior in some cases (e.g. working directory in compile commands might be virtual for some build systems like bazel).

When include-cleaner is invoked as `clang-include-cleaner foo.cc` the user is definitely trying to run this on a file relative to directory in which we invoked include-cleaner, hence we should make sure it's adressed through that path going forward.

Can we instead update logic near the following in `main`:
```cpp
 clang::tooling::ClangTool Tool(OptionsParser->getCompilations(),
                                 OptionsParser->getSourcePathList());
```

instead of passing `OptionsParser->getSourcePathList())`, we can turn all of these source paths into absolue paths, using the current-working-dir of the process, and then we don't need to worry about how they make their way into our ast-consumer.

https://github.com/llvm/llvm-project/pull/111375