Config option names outdated

[Tretgo]

The build options have been renamed from "build" to "board_build".

This is not reflected in the documentation, at least for STM32cube framework.

Warning! Ignore unknown configuration option build.stm32cube.disable_embedded_libs in section [env:robotdyn_blackpill_f303cc]

Using board_build.stm32cube.disable_embedded_libs = yes works as intended

[valeros]

Many thanks, fixed!