Add switch for KF5 (QT6) and Mod Cmake

if we want to test QET on QT6, KF5 must be removed from the code,
this switch is for that,

this is for testing only

sources/qetapp.cpp

@@ -42,7 +42,10 @@
 #define STRINGIFY(x) #x
 #include <QProcessEnvironment>
 #include <QRegularExpression>
-#include <KAutoSaveFile>
+#ifdef BUILD_WITHOUT_KF5
+#else
+#	include <KAutoSaveFile>
+#endif
 
 #ifdef QET_ALLOW_OVERRIDE_CED_OPTION
 QString QETApp::common_elements_dir = QString();
@@ -2080,6 +2083,9 @@ void QETApp::buildSystemTrayMenu()
 */
 void QETApp::checkBackupFiles()
 {
+#ifdef BUILD_WITHOUT_KF5
+	return;
+#else
 	QList<KAutoSaveFile *> stale_files = KAutoSaveFile::allStaleFiles();
 
 	//Remove from the list @stale_files, the stales file of opened project
@@ -2116,12 +2122,12 @@ void QETApp::checkBackupFiles()
 	}
 	for(const KAutoSaveFile *kasf : stale_files)
 	{
-#ifdef Q_OS_WIN
+#	ifdef Q_OS_WIN
 	//Remove the first character '/' before the name of the drive
 	text.append("<br>" + kasf->managedFile().path().remove(0,1));
-#else
+#	else
 	text.append("<br>" + kasf->managedFile().path());
-#endif
+#	endif
 	}
 
 	//Open backup file
@@ -2154,6 +2160,7 @@ void QETApp::checkBackupFiles()
 			delete stale;
 		}
 	}
+#endif
 }
 
 /**