There is a small mistake in assimp_view cmake file. On top you add ${DX9_INCLUDE_PATH} before you searched for DirectX. You can do this but then you have to run cmake configure twice. Just move the include command down, so it's working during the first configure process.
There are more mistakes in the mentioned cmake file. x64 is not supported. The appended new patch is for full a DX search.
Patch for cmake file
Modified cmake file