message: cmake: actually make use of WITH_LIBCXX variable.
  With that variable, set that appropriate CXX_FLAG flag.
diff: @@ -15,8 +15,8 @@ endif(NOT CMAKE_BUILD_TYPE)
  option(
  WITH_LIBCXX
  - "Building with clang++ and libc++(in Linux). To enable with: -DWITH_LIBCXX=On"
  - On)
  + "If buildling with clang++ and libc++(in Linux). To enable with: -DWITH_LIBCXX=On"
  + Off)
  project(SURELOG)
  @@ -28,6 +28,10 @@ set(CMAKE_CXX_STANDARD 17)
  set(CMAKE_CXX_STANDARD_REQUIRED ON)
  set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
  +if(WITH_LIBCXX)
  + set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
  +endif()
  +
  set(FLATBUFFERS_BUILD_TESTS OFF CACHE BOOL "Skip flatbuffers' tests")
  add_subdirectory(third_party/flatbuffers EXCLUDE_FROM_ALL)
  