To install x86_64-w64-mingw32-gcc, run the following command in macOS terminal (Applications->Utilities->Terminal)
sudo port install x86_64-w64-mingw32-gcc
To see what files were installed by x86_64-w64-mingw32-gcc, run:
port contents x86_64-w64-mingw32-gcc
To later upgrade x86_64-w64-mingw32-gcc, run:
sudo port selfupdate && sudo port upgrade x86_64-w64-mingw32-gcc
Reporting an issue on MacPorts Trac
The MacPorts Project uses a system called Trac to file tickets to report bugs and enhancement requests.
Though anyone may search Trac for tickets, you must have a GitHub account in order to login to Trac to create tickets.