Switch SAMD51 back to -Os
Switch SAMD51 back to -Os

It messes up neopixel timing otherwise.

Fixes #1326
adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython