Avoid name mangling ref: http://qiita.com/items/4f966648fbcf9edfc143

file0.txt

#include <iostream>
int add(int a, int b){  
    return a+b;
}
int main(void){ 
    std::cout << add(1,2) << std::endl;
    return 0;
}

file1.txt

0000000100000d00 T __Z3addii
// 省略
0000000100000d50 T _main
// 省略

file2.txt

extern "C" int add(int, int);