ci: Build macOS 10.13+ package as C++17

Take advantage of the standard library implementations of those C++17
features available when targeting macOS 10.13.  Note that the standard
library `std::filesystem` implementation is not available until 10.15.

.gitlab/ci/configure_macos_package.cmake

@@ -1,6 +1,6 @@
 set(CPACK_SYSTEM_NAME "macos-universal" CACHE STRING "")
 set(CMAKE_OSX_DEPLOYMENT_TARGET "10.13" CACHE STRING "")
 set(CMAKE_C_STANDARD "11" CACHE STRING "")
-set(CMAKE_CXX_STANDARD "14" CACHE STRING "")
+set(CMAKE_CXX_STANDARD "17" CACHE STRING "")
 
 include("${CMAKE_CURRENT_LIST_DIR}/configure_macos_package_common.cmake")