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/abstracteditorsupport.cpp

@@ -27,6 +27,7 @@
 
 #include "cppfilesettingspage.h"
 #include "cppmodelmanager.h"
+#include "cpptools/cpptoolsplugin.h"
 
 #include <utils/fileutils.h>
 #include <utils/macroexpander.h>
@@ -68,5 +69,10 @@ QString AbstractEditorSupport::licenseTemplate(const QString &file, const QStrin
     return Utils::TemplateEngine::processText(&expander, license, nullptr);
 }
 
+bool AbstractEditorSupport::usePragmaOnce()
+{
+    return Internal::CppToolsPlugin::instance()->usePragmaOnce();
+}
+
 } // namespace CppTools