CMake generator full path

Normally it is not necessary to specify the path to the CMake generator backend, assuming the generator executable is on the system PATH. For special use cases such as testing CMake with different versions of a generator the generator executable absolute path may be specified via CMAKE_MAKE_PROGRAM. The absolute path to the generator is necessary or CMake will not find it.

Example: GitHub Actions Linux image:

    - name: Install Ninja
      run: |
        curl -O

    - name: CMake configure
      run: cmake -G Ninja -DCMAKE_MAKE_PROGRAM=$(realpath ./ninja) -Bbuild

Get the full path from a relative path with realpath to Ninja (when necessary) like:

cmake -G Ninja -DCMAKE_MAKE_PROGRAM=$(realpath ./ninja)

On MacOS use Homebrew to install Ninja:

brew install ninja

On Windows use MSYS2 or pip install ninja.