Add test application / CI build step

libcpp: need to add a test application that links against the libraries to check for potential problems like the mach_absolute_time missing symbol at link time due to poor symbol definition. This application should be built as a test, and not when we are being used as a subproject.

未指定文件或测试。首先检查仓库现有的构建配置和 CI 入口点，以了解测试和子项目的处理方式；完成的标准是：测试应用程序与这些库进行链接，能够捕获链接时的符号问题，在 CI 中运行，并且在将 libcpp 作为子项目使用时不会构建。

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