You need to read the code you’re compiling. The main.c expects you to define -DF1 if you are compiling for a STM32F1 board, this is done via build_flags in the original example. So, just add build_flags = -DF1 to your platformio.ini. Also check if you need to change the blink pin as it’s currently set to PA5. (You’d need to check the discovery board’s schematics for that).
If that error appears again there’s probably something wrong with the reset_config in OpenOCD. You may try to: Hold down the reset button before the upload is started, and release it when OpenOCD starts up (at the right time), or modify the reset_config in the OpenOCD config files for your board (which you can find out by doing a “Verbose Upload” and looking at the -f *.cfg flags in the openocd command). There are threads about that (STM32F411CE (BlackPill) + STLink V2 + Arduino on Ubuntu - #2 by maxgerhardt)