kconfig_compiler: add override to generated destructors
This fixes the clang warning globalsettings_kmail.h:58:5: warning: '~GlobalSettingsBase' overrides a destructor but is not marked 'override' [-Wsuggest-destructor-override]
This fixes the clang warning globalsettings_kmail.h:58:5: warning: '~GlobalSettingsBase' overrides a destructor but is not marked 'override' [-Wsuggest-destructor-override]