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

src/V3Clock.cpp

@@ -273,12 +273,11 @@ private:
     }
     virtual void visit(AstNodeModule* nodep) override {
         // UINFO(4, " MOD   " << nodep << endl);
-        AstNodeModule* origModp = m_modp;
+        VL_RESTORER(m_modp);
         {
             m_modp = nodep;
             iterateChildren(nodep);
         }
-        m_modp = origModp;
     }
     virtual void visit(AstScope* nodep) override {
         // UINFO(4, " SCOPE   " << nodep << endl);