Clang: Use follow symbol result from clang when global fails

When built-in code model fails to follow symbol under cursor
fall back to the clang result even if it only follows
to the decalration.

Change-Id: I22d8c5fee6ab7594b1d1b7ce8104414db28383c7
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cppsymbolinfo.h

@@ -39,6 +39,7 @@ public:
     int endLine = 0;
     int endColumn = 0;
     QString fileName;
+    bool isPureDeclarationForUsage = false;
 };
 
 } // namespace CppTools