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STMF103 is the only one with decent support and it's an old chip.
There's a few threads on the other forum that starts with eev about starting ARM Cortex development with free tools. I haven't tried it in about 6 years though, so no idea. I still pay for Crossworks. OpenSTM32 looks pretty good. There's so many compilers and programmers, it's tough to get started.
I don't think that means none, it means you have no other option than serial and there are no ports available.
Mine is different. Maybe my Arduino IDE is older. I don't get the option of the discovery as a target, only the Star OTTO. When I installed STM32F4 board to test, the installer loaded an STM32 USB driver. With the driver installed when plugged into the STM32 USB, you should get a serial port available.