CMake: Build with -std:c++latest for MSVC

Making CMake match MSBuild in this aspect will hopefully
reduce how often we accidentally break the MSVC CMake build.

Source/CMakeLists.txt

@@ -16,7 +16,13 @@ if(CMAKE_SYSTEM_NAME MATCHES "Windows")
   add_definitions(-D_SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING)
 endif()
 
+if (MSVC)
+  set(CMAKE_CXX_STANDARD 20)
+  set(CMAKE_CXX20_STANDARD_COMPILE_OPTION "-std:c++latest")
+else()
   set(CMAKE_CXX_STANDARD 17)
+endif()
+
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)