Calling external C codes in MATLAB Function block

Hi, I am modeling an automotive system in Simulink. There are large amount of pre-written C codes which I have to call them in MATLAB Function blocks. As far as I know there are different methods to call an external function in MATLAB, like making MEX file or using Legacy Code Tool. Also I recently noticed that coder.ceval function is used in some similar cases. Since there several C code files and they have also dependencies, I am not sure which one is more efficient or possible in this case. Any idea would be greatly appreciated. Thanks.