unix/moduselect: Don't allow both posix and non-posix configurations.
unix/moduselect: Don't allow both posix and non-posix configurations.

Signed-off-by: Jim Mussared <e84f5c941266186d0c97dcc873413469b954847e@gmail.com>

adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,bvernoux/micropython,bvernoux/micropython,bvernoux/micropython,adafruit/circuitpython,henriknelson/micropython,bvernoux/micropython,adafruit/circuitpython,bvernoux/micropython