header files change would not trigger rebuild

现象之一：jenkins直接调用internal_build脚本make，木有make clean，导致`改动.h文件中的接口，没有改变.cc文件中的调用`这种情况不会重新make。出现标记为失败情况被错误标记为成功。暂时在internal_build里加了一个make clean。感觉需要修改一下Makefile彻底解决问题。

Inspect the internal_build script and the Makefile to understand how Jenkins invokes make without make clean and how header dependencies are tracked. Reproduce the header-only interface change described in the issue, then verify that the affected .cc file rebuilds and that failures are not incorrectly reported as successful.

Written by the indexing model from the issue text.