STM32: Default Flash Configuration Used - See Override Flash Size Designator #1573

[spi3ex]

https://cwiki.apache.org/confluence/display/NUTTX/Configuration+Variables

In file included from chip/stm32_flash.c:38:
chip/stm32f20xxf40xx_flash.c:51:4: warning: #warning "Default Flash Configuration Used - See Override Flash Size Designator" [-Wcpp]
51 | # warning "Default Flash Configuration Used - See Override Flash Size Designator"
| ^~~~~~~