如何根据configure file / makefile文件删除死代码或无用代码

When we compile a C/C++ project, some files and codes in the project source are not needed for compilation. For example, test folder (some testing scripts), examples folder and dead code. How can I recognize these source files that are not compiled to binary files? It is not hoped that compiling is necessary. Cause I need to process many projects automatically and it is really hard to compile all projects without manual operations.When we compile a C/C++ project, some files and