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

[Byoungchan Lee via cfe-commits]

bc-lee wrote:

> in our case this is symlinked to an immutable copy of the source file (to make sure builds don't act weird if you edit some sources while the build is running). hence it'll be a regression.
> 
> What's the concern about not performing this directly as relative to the process' working directory? That approach doesn't rely on any assumptions about the build system, or filesystem layout hence feels much more robust.

It’s unfortunate that we can't apply unified logic for determining the actual output file. It's especially disappointing given that I’m using GN and you’re using Bazel, both of which are build systems from Google.

I’ve adjusted the logic to find the correct output directory before the compiler invocation starts. Please take another look and let me know if there's anything else I should consider.

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