Why am I warned that the 'CMAKE_ TOOLCHAIN_ FILE' variable is not used by the project?

problem ：

When I build some third-party code, I am seeing the following warning from CMake: When I build some third-party code , I see from CMake The following warnings for ：

CMake Warning:  Manually-specified variables were not used by the project:    CMAKE_TOOLCHAIN_FILE

What is causing this warning? What caused this warning ？I checked the configuration files, but could not find anywhere where this variable is defined. I checked the configuration file , But nowhere to define this variable .

Should I be concerned about this warning? Should I worry about this warning ？How can I fix it so that the warning goes away? How to fix it so that the warning disappears ？

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Solution ：

Reference resources ： https://stackoom.com/en/question/zv6I