support bazel complie this project and format code.

basic_content/const/extern_const/const_file2.cpp

@@ -1,11 +1,8 @@
-#include<iostream>
+#include <iostream>
 /**
  * by 光城
  * compile: g++ -o file const_file2.cpp const_file1.cpp
  * execute: ./file
  */
 extern const int ext;
-int main(){
-
-    std::cout<<ext<<std::endl;
-}
+int main() { std::cout << ext << std::endl; }