Clang: Warn of potentially expensive checks

...for the code model.

If a diagnostic configuration with potentially expensive checks is
selected in Options/Preferences > C++ > Code Model, show a warning below
the combo box.

Change-Id: I52c5c2e229fd50c0fd82f70154fb5b727726ba31
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/clangtools/clangtoolsplugin.cpp

@@ -73,7 +73,7 @@ class ClangToolsOptionsPage : public Core::IOptionsPage
 public:
     explicit ClangToolsOptionsPage()
     {
-        setId("Analyzer.ClangTools.Settings");
+        setId(Constants::SETTINGS_PAGE_ID);
         setDisplayName(QCoreApplication::translate(
                            "ClangTools::Internal::ClangToolsOptionsPage",
                            "Clang Tools"));