CMakeLists.txt: Replace some mistaken uses of `CMAKE_SOURCE_DIR` with `CMAKE_CURRENT_SOURCE_DIR`.
CMakeLists.txt: Replace some mistaken uses of `CMAKE_SOURCE_DIR` with `CMAKE_CURRENT_SOURCE_DIR`.

nanshe-org/rank_filter,DudLab/rank_filter,nanshe-org/rank_filter,DudLab/rank_filter,nanshe-org/rank_filter,jakirkham/rank_filter,DudLab/rank_filter,jakirkham/rank_filter,jakirkham/rank_filter