Use C++17

CMakeLists.txt

@@ -4,6 +4,8 @@ project(kdegraphics-thumbnailers)
 set(QT_MIN_VERSION "5.15.2")
 set(KF5_MIN_VERSION "5.90.0")
 set(KDE_COMPILERSETTINGS_LEVEL "5.82")
+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})