CMAKE_SOURCE_DIR vs. CMAKE_CURRENT_SOURCE_DIR usage in studio 3.4 timeframe

[ggfan]

This is just a heads-up, from:
android/ndk-samples#597

Studio 3.4 is going to create an internal CMake Project, from which calling application's top level CMakeLists.txt. Mathfu might need to verify its use of CMAKE_SOURCE_DIR is not affected.