CompilationDatabaseProjectManager: Incorrect folder structure when multiple directories with same name exist

The CompilationDatabaseProjectManager plugin does not correctly build up the directory hierarchy when multiple directories with the same name exist within the project's directory hierarchy. I have created a small sample project to demonstrate this:

Steps to reproduce:

1) enable the experimental CompilationDatabaseProjectManager plugin
2) save the attached tar archive `testproject.tar.gz` in the `/tmp/` directory
3) `cd /tmp/`
4) extract the tar archive: `tar -xavf testproject.tar.gz`
5) load the test project into Qt Creator (right click in "Projects" view -> "Load Project" -> select File `/tmp/testproject/compile_commands.json`)
6) observe the directory structure in the project view

Result:

The directory structure is displayed incorrectly. There is no top-level `vcl` directory, but the `vcl/qt5/second.cxx` tree is shown underneath `canvas/source`.

The attached screenshot `screenshot_incorrect_directory_structure.png` shows this.

Expected result:

The original file tree hierarchy should be represented in the project view.

There should be a top-level `vcl` directory containing a `qt5` subdirectory, which in turn contains the file `second.cxx`, besides `canvas/source/vcl/first.cxx`.

Note: Instead of extracting the test project into `/tmp/`, any other directory can be chosen as well. However, the compilation database `compile_commands.json` needs to be recreated in this case (e.g. by running `bear make`), since it contains absolute path names.