CMake build system: Duplicated include paths

Like the qmake and qbs build systems fro Qt Creator, the CMake build system has to collect include directories and add them to lists.
The CMake build system has the weakness, that it adds several paths which in canonical form would be one and the same. For example instead of adding /foo once, it adds /foo/bar1/.. /foo/bar2/.. /foo/bar3/.., etc.

That leads to duplicated imports in the code completion:

...and to duplicated paths in the code model:

...and of course to a big build.ninja file, since the duplications happen for each compile unit: