That is not an error. It is telling you that MinGW is set up as your compiler, and it is giving you a warning that if you have existing mex code that was developed assuming that pointers are 32 bits, that you will need to update your code. MATLAB started supporting 64 bit mex about a decade ago or so, so this is a warning for the situation where you are dealing with fairly old code.
The message you are getting is telling you that the setup functioned, and you should go ahead and use mex to build the functions.
