message: cmake: ensure C++17 is default
diff: +# setting defaults
  +set(CMAKE_CXX_STANDARD 17)
  +set(CMAKE_CXX_STANDARD_REQUIRED ON)
  +set(CMAKE_CXX_EXTENSIONS OFF)
  +
  if(NOT CMAKE_TOOLCHAIN_FILE)
  set(CMAKE_TOOLCHAIN_FILE "${CMAKE_CURRENT_LIST_DIR}/toolchains/cxx17.cmake"
  CACHE FILEPATH "Path to CMake toolchain file")
  