4.8.0 QtScript JavaScriptCore causes compilation error for GCC 4.7.0

Compilation of 4.8.0 with GCC 4.7.0 breaks due to errors in

• src/3rdparty/javascriptcore/JavaScriptCore/runtime/JSStaticScopeObject.h
• src/3rdparty/javascriptcore/JavaScriptCore/runtime/JSGlobalObject.h

Proposed fixes:

• src/3rdparty/javascriptcore/JavaScriptCore/runtime/JSStaticScopeObject.h

  + class JSGlobalObject : public JSVariableObject {
  + protected:
  +- using JSVariableObject::JSVariableObjectData;
  +-
  +- struct JSGlobalObjectData : public JSVariableObjectData {
  ++ struct JSGlobalObjectData : public JSVariableObject::JSVariableObjectData

  { + // We use an explicit destructor function pointer instead of a + // virtual destructor because we want to avoid adding a vtable + // pointer to this struct. Adding a vtable pointer would force the {cocde}