First: don’t use the STDPeriph, it’s deprecated. Use the HAL.
Second: it’s asking you to define in the library itself what platform it is compiling for so it can include the correct dependencies. (Such as peripheral placements in memory)
The solution is to read the STM chip’s model number (something like STM32F103C8T6) then look inside the stm32f10x.h file and select your MCU, which probably involves uncommenting a define line. If you can’t figure out what types of options there are, try reading the datasheet for the MCU you have as it specifies everything about it.
For the EVAL board you can select any of them as they only alias (define) simple names such as LED1. You just can’t use them then.
BUT AGAIN DON’T USE STDPeriph use the HAL! Just use CubeMX to generate a project with libraries for you. It probably also better supports the BluePill than some old STDPeriph eval board header.
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