cmake add_subdirectory(SYSTEM) examples

ossia/score 3rdparty/mimalloc.cmake :24 

add_subdirectory(3rdparty/snmalloc EXCLUDE_FROM_ALL SYSTEM)

ossia/score 3rdparty/vst3.cmake :54 

add_subdirectory("${VST3_SDK_ROOT}" "${CMAKE_BINARY_DIR}/vst3" SYSTEM)