Small Change on the CMakeLists in order to include the library in other projects using fetch_content

[hporro]

When I include the cuNSearch in other projects using fetch_content, the folders ${CMAKE_BINARY_DIR} and ${CMAKE_CURRENT_BINARY_DIR} are different, and the cmake target cuNSearch does not include the correct folder.

I think this would be a good fix for that, without breaking any other project.