Internals: Use C++11 = default where obvious. No functional change intended.

src/V3PreShell.cpp

@@ -151,8 +151,8 @@ private:
 
 public:
     // CONSTRUCTORS
-    V3PreShellImp() {}
-    ~V3PreShellImp() {}
+    V3PreShellImp() = default;
+    ~V3PreShellImp() = default;
 };
 
 V3PreShellImp V3PreShellImp::s_preImp;