unix: Fix build on arm64-darwin due to integer cast.
unix: Fix build on arm64-darwin due to integer cast.

This fixes error: cast to smaller integer type 'int' from 'pthread_t'.
pthread_t is defined as long, not as int.

Signed-off-by: Pavol Rusnak <ab8bc2c6388fa63c7ac477230cd3c9c8f17be98b@rusnak.io>

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