If you're attempting to use the MinGW compiler with VeriStand 2019 R2 or earlier, you're likely encountering a compatibility issue between VeriStand, MATLAB, and MinGW. MinGW is only compatible with VeriStand 2019 R3 or later, while the latest version of MATLAB compatible with VeriStand 2019 R2 or earlier is MATLAB 2018a. This compatibility chart
is the best resource for determining which compilers and versions of VeriStand/MATLAB you will need to compile Simulink models into .DLLs for different operating systems. In this particular case, you would need to either upgrade VeriStand to 2019 R3 or later, or install and use the Windows SDK 7.1 compiler to compile your model.