Wizards: Support using #pragma once instead of include guards

Allow users to choose #pragma once instead of #ifndef include guards in
generated header files.

Fixes: QTCREATORBUG-12166
Change-Id: I3ba41c7570beb9c5958e174b5581fcc25855050f
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Filip Bucek <fbucek@atlas.cz>

src/plugins/cpptools/cppfilesettingspage.h

@@ -42,16 +42,15 @@ namespace Ui { class CppFileSettingsPage; }
 
 struct CppFileSettings
 {
-    CppFileSettings();
-
     QStringList headerPrefixes;
     QString headerSuffix;
     QStringList headerSearchPaths;
     QStringList sourcePrefixes;
     QString sourceSuffix;
     QStringList sourceSearchPaths;
-    bool lowerCaseFiles;
     QString licenseTemplatePath;
+    bool headerPragmaOnce = false;
+    bool lowerCaseFiles = false;
 
     void toSettings(QSettings *) const;
     void fromSettings(QSettings *);