Wrong cxx compiler detection when using ninja generator with CMake

If Qt Creator is used to open a CMake project and the ninja generator is selected it fails to find the correct compiler.

This happens only if there is another compiler installed on the system whichs path is in the system's PATH variable.

An example:
If the selected Qt Kit contains the visual studio compiler and there is another compiler installed on the system (e.g.: http://strawberryperl.com/). In this case, the strawberry's c compiler is found by CMake becaus there are the strawberry compiler paths in the system's path variable.

A workaround is to remove the paths of the other compiler from the system's PATH variable.