Add required CXX standards to the main CMakeLists file

CMakeLists.txt

@@ -3,6 +3,10 @@
 # === Preamble ===
 cmake_minimum_required(VERSION 3.12...3.19.1)
 
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+
 # Make the 'cmake' module directory visible to CMake.
 list( APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake )