Thank you very much! It worked perfectly for me!
My .ini file became this in my configurations:
[env:genericSTM32F103C8]
platform = https://github.com/platformio/platform-ststm32.git
board = genericSTM32F103C8
framework = arduino
lib_extra_dirs = ~/Documents/Arduino/libraries
upload_protocol = stlink
upload_flags = -c set CPUTAPID 0x2ba01477