Internals: Use VL_RESTORER class to save/restore vars. No functional change intended.

src/V3Clean.cpp

@@ -171,12 +171,11 @@ private:
 
     // VISITORS
     virtual void visit(AstNodeModule* nodep) override {
-        AstNodeModule* origModp = m_modp;
+        VL_RESTORER(m_modp);
         {
             m_modp = nodep;
             iterateChildren(nodep);
         }
-        m_modp = origModp;
     }
     virtual void visit(AstNodeUniop* nodep) override {
         iterateChildren(nodep);