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

[kadir çetinkaya via cfe-commits]

kadircet wrote:

> so clang-include-cleaner correctly adjusted the path to /home/leebc/.cache/bazel/_bazel_leebc/5ea2deb937e75f0bf29ba4c49931e67d/execroot/_main/api/main.cc, which was correctly symlinked.

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.

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