support bazel complie this project and format code.

practical_exercises/10_day_practice/day5/virtual/example2.cpp

@@ -0,0 +1,17 @@
+/* 例2.cpp */
+#include <iostream>
+using namespace std;
+class A {
+public:
+  void vf() { cout << "I come from class A" << endl; }
+};
+class B : virtual public A {};
+class C : virtual public A {};
+class D : public B, public C {};
+
+int main() {
+  D d;
+  d.vf(); // okay
+  
+  return 0;
+}