Fix warnings about unused members in some clang-related classes

Change-Id: I564ac810ed8ae950e9ced54358929358379bfffb
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangrefactoring/refactoringengine.cpp

@@ -56,6 +56,7 @@ RefactoringEngine::RefactoringEngine(ClangBackEnd::RefactoringServerInterface &s
       m_filePathCache(filePathCache),
       m_symbolQuery(symbolQuery)
 {
+    Q_UNUSED(m_client)
 }
 
 RefactoringEngine::~RefactoringEngine() = default;