Utils: Collapse most of porting,h

Taking the Qt 6 branches, leaving some dummies until downstream
adapted.

Change-Id: Ib9b86568d73c341c8f740ba497c3cbfab830d8a1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/cppcheck/cppcheckdiagnostic.h

@@ -50,7 +50,7 @@ public:
     int lineNumber = 0;
 };
 
-Utils::QHashValueType qHash(const Diagnostic &diagnostic);
+size_t qHash(const Diagnostic &diagnostic);
 
 } // namespace Internal
 } // namespace Cppcheck