Internals: Use and enforce class final for ~5% performance boost.

src/V3CCtors.cpp

@@ -34,7 +34,7 @@
 #include <algorithm>
 #include <map>
 
-class V3CCtorsVisitor {
+class V3CCtorsVisitor final {
 private:
     string m_basename;
     string m_argsp;