support bazel complie this project and format code.

basic_content/const/extern_const/file2.cpp

@@ -1,11 +1,8 @@
-#include<iostream>
+#include <iostream>
 /**
  * by 光城
  * compile: g++ -o file file2.cpp file1.cpp
  * execute: ./file
  */
 extern int ext;
-int main(){
-
-    std::cout<<(ext+10)<<std::endl;
-}
+int main() { std::cout << (ext + 10) << std::endl; }