py/mkrules.mk: Rework find command so it works on OSX.
py/mkrules.mk: Rework find command so it works on OSX.

The Mac version of find doesn't support -printf, so this changes
things to use sed to strip off the leading path element instead.

adafruit/circuitpython,bvernoux/micropython,adafruit/circuitpython,alex-robbins/micropython,Timmenem/micropython,micropython/micropython-esp32,henriknelson/micropython,oopy/micropython,henriknelson/micropython,TDAbboud/micropython,blazewicz/micropython,pozetroninc/micropython,blazewicz/micropython,Timmenem/micropython,oopy/micropython,adafruit/micropython,dmazzella/micropython,cwyark/micropython,hiway/micropython,pramasoul/micropython,trezor/micropython,SHA2017-badge/micropython-esp32,MrSurly/micropython,adafruit/micropython,TDAbboud/micropython,lowRISC/micropython,puuu/micropython,pfalcon/micropython,tobbad/micropython,TDAbboud/micropython,tobbad/micropython,pfalcon/micropython,toolmacher/micropython,MrSurly/micropython,torwag/micropython,tralamazza/micropython,pramasoul/micropython,Peetz0r/micropython-esp32,ryannathans/micropython,pozetroninc/micropython,blazewicz/micropython,pozetroninc/micropython,MrSurly/micropython-esp32,ryannathans/micropython,infinnovation/micropython,PappaPeppar/micropython,alex-robbins/micropython,torwag/micropython,tuc-osg/micropython,alex-robbins/micropython,Peetz0r/micropython-esp32,hiway/micropython,adafruit/micropython,alex-robbins/micropython,mhoffma/micropython,chrisdearman/micropython,HenrikSolver/micropython,chrisdearman/micropython,kerneltask/micropython,kerneltask/micropython,tuc-osg/micropython,mhoffma/micropython,bvernoux/micropython,lowRISC/micropython,blazewicz/micropython,oopy/micropython,MrSurly/micropython-esp32,selste/micropython,HenrikSolver/micropython,toolmacher/micropython,mhoffma/micropython,adafruit/circuitpython,micropython/micropython-esp32,blazewicz/micropython,trezor/micropython,pramasoul/micropython,pfalcon/micropython,tralamazza/micropython,lowRISC/micropython,AriZuu/micropython,PappaPeppar/micropython,tralamazza/micropython,cwyark/micropython,PappaPeppar/micropython,HenrikSolver/micropython,toolmacher/micropython,TDAbboud/micropython,torwag/micropython,micropython/micropython-esp32,deshipu/micropython,dmazzella/micropython,trezor/micropython,pfalcon/micropython,AriZuu/micropython,ryannathans/micropython,ryannathans/micropython,pozetroninc/micropython,MrSurly/micropython,PappaPeppar/micropython,henriknelson/micropython,MrSurly/micropython,dmazzella/micropython,pfalcon/micropython,hiway/micropython,dmazzella/micropython,puuu/micropython,oopy/micropython,infinnovation/micropython,bvernoux/micropython,selste/micropython,tobbad/micropython,alex-robbins/micropython,chrisdearman/micropython,AriZuu/micropython,Peetz0r/micropython-esp32,Timmenem/micropython,pramasoul/micropython,adafruit/circuitpython,cwyark/micropython,hiway/micropython,torwag/micropython,Peetz0r/micropython-esp32,AriZuu/micropython,tobbad/micropython,chrisdearman/micropython,swegener/micropython,selste/micropython,SHA2017-badge/micropython-esp32,infinnovation/micropython,toolmacher/micropython,HenrikSolver/micropython,trezor/micropython,bvernoux/micropython,kerneltask/micropython,hiway/micropython,MrSurly/micropython-esp32,puuu/micropython,SHA2017-badge/micropython-esp32,mhoffma/micropython,trezor/micropython,ryannathans/micropython,tralamazza/micropython,swegener/micropython,puuu/micropython,micropython/micropython-esp32,lowRISC/micropython,selste/micropython,Timmenem/micropython,deshipu/micropython,Timmenem/micropython,cwyark/micropython,TDAbboud/micropython,deshipu/micropython,MrSurly/micropython-esp32,tuc-osg/micropython,oopy/micropython,henriknelson/micropython,lowRISC/micropython,SHA2017-badge/micropython-esp32,infinnovation/micropython,selste/micropython,toolmacher/micropython,puuu/micropython,adafruit/circuitpython,swegener/micropython,adafruit/micropython,pramasoul/micropython,swegener/micropython,PappaPeppar/micropython,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,torwag/micropython,deshipu/micropython,kerneltask/micropython,micropython/micropython-esp32,adafruit/micropython,pozetroninc/micropython,MrSurly/micropython,adafruit/circuitpython,mhoffma/micropython,tuc-osg/micropython,swegener/micropython,chrisdearman/micropython,tobbad/micropython,HenrikSolver/micropython,henriknelson/micropython,deshipu/micropython,tuc-osg/micropython,cwyark/micropython,kerneltask/micropython,infinnovation/micropython,bvernoux/micropython,Peetz0r/micropython-esp32,AriZuu/micropython