Clang: Fix built-in's ExtractFunction action

Since

  Clang: Provide highlighting for identifier under cursor
  commit ca72c29462

the LocalUseMap, used for some refactoring actions, was not updated
anymore. Fall back to the built-in implementation for the LocalUseMap
because it contains pointers to built-in AST that clang obviously can't
provide.

Task-number: QTCREATORBUG-18607
Change-Id: I08762fe457835d4d83aca719febcb3497ee9696b
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Robert Loehning <robert.loehning@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/cpptools/builtincursorinfo.h

@@ -26,17 +26,21 @@
 #pragma once
 
 #include "cppcursorinfo.h"
+#include "cpptools_global.h"
+
+#include <cplusplus/CppDocument.h>
 
 #include <QFuture>
 
 namespace CppTools {
-namespace Internal {
 
-class BuiltinCursorInfo
+class CPPTOOLS_EXPORT BuiltinCursorInfo
 {
 public:
     static QFuture<CursorInfo> run(const CursorInfoParams &params);
+
+    static CppTools::SemanticInfo::LocalUseMap
+    findLocalUses(const CPlusPlus::Document::Ptr &document, int line, int column);
 };
 
-} // namespace Internal
 } // namespace CppTools