tools/make-frozen.py: Allow to run with no directory passed in.
tools/make-frozen.py: Allow to run with no directory passed in.

In which case it will just emit empty frozen C definitions.

tobbad/micropython,trezor/micropython,kerneltask/micropython,pozetroninc/micropython,tobbad/micropython,MrSurly/micropython,MrSurly/micropython,tobbad/micropython,henriknelson/micropython,MrSurly/micropython,bvernoux/micropython,henriknelson/micropython,pramasoul/micropython,pramasoul/micropython,pozetroninc/micropython,selste/micropython,tobbad/micropython,selste/micropython,adafruit/circuitpython,MrSurly/micropython,kerneltask/micropython,kerneltask/micropython,henriknelson/micropython,trezor/micropython,pozetroninc/micropython,henriknelson/micropython,kerneltask/micropython,bvernoux/micropython,bvernoux/micropython,pozetroninc/micropython,trezor/micropython,pramasoul/micropython,selste/micropython,adafruit/circuitpython,pramasoul/micropython,pozetroninc/micropython,selste/micropython,MrSurly/micropython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,kerneltask/micropython,trezor/micropython,trezor/micropython,tobbad/micropython,adafruit/circuitpython,selste/micropython,pramasoul/micropython,bvernoux/micropython,bvernoux/micropython