I have MinGW-w64 installed (via GitHub - niXman/mingw-builds-binaries: MinGW-W64 compiler binaries) but as juliac hardcodes cc, it won’t be used.
I first had to manually add the bath to the cc.exe of MinGW to Windows’ PATH environment variable.
So there should be something done, either an option to juliac to specify the path to the compiler executable or Julia’s installer gets an option to install MinGW and then sets up the environment variables directly.