More robust common_config_file_iterator

common_config_file_iterator::common_config_file_iterator has a little problem: One of the args is std::set, which is incompatible between libc++ and libstdc++. As a result, the function, if compiled with {GCC, Clang}, is incompatible with {Clang, GCC). This can be fixed without breaking anything by moving it to the header part and declaring it static. What are your opinions about it?

定位 common_config_file_iterator 的声明和定义，然后检查其 std::set 参数如何跨越编译接口。比较使用 GCC 和 Clang 的构建，并验证将实现移到 header 中并将其声明为 static 能够保持兼容性。当迭代器可以在这些编译器组合中使用且不会出现报告的不兼容问题时，即视为完成。

由索引模型根据 Issue 内容生成。