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Use `try_compile` instead of `try_run`. It is not clear why `try_run` was ever needed, and it does not work during cross-compiling. Update the check's source file to remove code associated with actually running things. Also remove the ancient `__CLASSIC_C__` code path and use a simple `int main(void)` as in `Modules/CheckIncludeFile.c.in`. Fixes: #16920
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