Makes building the DirectX 9 sample optional, auto detects if it should be built only if DirectX is installed.
Removes the linking of DirectX libraries to all samples which do not require it.
Merge branch 'feature/optional-build-directx-samples' into merge-test

* feature/optional-build-directx-samples:
  Makes building the DirectX 9 sample optional, auto detects if it should be built only if DirectX is installed. Removes the linking of DirectX libraries to all samples which do not require it.