Require C++17

It's reasonable to use it at this point and Plasma and many KDE apps do already

CMakeLists.txt

@@ -10,6 +10,9 @@ project(ark VERSION ${RELEASE_SERVICE_VERSION})
 set(QT_MIN_VERSION 5.12.0)
 set(KF5_MIN_VERSION 5.77.0)
 
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
 find_package(ECM ${KF5_MIN_VERSION} REQUIRED NO_MODULE)
 set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules)