C++: Fix unused field warnings in test.

Change-Id: I898668a91eb7d3fa18c0a8d3e7e7507f0fb5a917
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

tests/auto/cplusplus/preprocessor/tst_preprocessor.cpp

@@ -147,6 +147,8 @@ public:
     {
 #if 1
         m_recordedIncludes.append(Include(includedFileName, mode, line));
+        Q_UNUSED(m_env);
+        Q_UNUSED(m_includeDepth);
 #else
         Q_UNUSED(line);