Arduino IDE support Cortex-M ARM architecture and although STM32 is not “officially” included stm32duino.com has all the resources to add support for STM32 boards in Arduino.
This forum post explains what should be done step by step to setup and use OLIMEXINO-STM32 board with Arduino IDE.
Nov 09, 2018 @ 16:06:13
I changed the USB bootloader for STM32 bluepills to increase the time to wait for a new firmware to 10 seconds, avec flashed them with stm32flash, not with some proprietary tool from ST, using a USB-serial dongle:
http://www.zoobab.com/bluepill-arduinoide
The other flashing stm32loader in python did not work for me.
Will try on the Olimex STM32-H103 to see if I can do the same.