What I've tried to do:
1. Run configure with a similar processor: ./tools/configure.sh -l
nucleo-f4x1re:f401-nsh
2. Change the system type via menuconfig(System Type -> STM32 Chip
Selection, select STM32F405RG)
When you did this your CONFIG_MM_REGIONS settings became wrong (becuase
the ST32F405 needs two memory regions) and you lost the board selection
The board selections depends on the MCU selection so changing that
invalidates the previous board selection.
LN: arch/arm/src/board to /home/robert/nuttx//src
No directory at /home/robert/nuttx//src
make[1]: *** [tools/Unix.mk:300: arch/arm/src/board] Error 1
make: *** [too ls/Unix.mk:684: menuconfig] Error 2
That is because you lost the selected board when you changed the MCU.
The path that is echoed as /home/robert/nuttx//src is wrong because
there is no board directory in the path because there no board selected.
