unix: Support #if-able impl-specific cmdline options.
unix: Support #if-able impl-specific cmdline options.

For example, we still build w/o GC enabled, so cannot really set heap size.

noahchense/micropython,dinau/micropython,blazewicz/micropython,rubencabrera/micropython,danicampora/micropython,mgyenik/micropython,suda/micropython,emfcamp/micropython,infinnovation/micropython,orionrobots/micropython,vitiral/micropython,aitjcize/micropython,jimkmc/micropython,xhat/micropython,matthewelse/micropython,dinau/micropython,Peetz0r/micropython-esp32,misterdanb/micropython,cnoviello/micropython,mgyenik/micropython,martinribelotta/micropython,chrisdearman/micropython,tralamazza/micropython,supergis/micropython,ruffy91/micropython,stonegithubs/micropython,MrSurly/micropython,martinribelotta/micropython,noahwilliamsson/micropython,xhat/micropython,SHA2017-badge/micropython-esp32,TDAbboud/micropython,infinnovation/micropython,warner83/micropython,SHA2017-badge/micropython-esp32,xyb/micropython,henriknelson/micropython,praemdonck/micropython,trezor/micropython,KISSMonX/micropython,cwyark/micropython,mpalomer/micropython,alex-robbins/micropython,rubencabrera/micropython,utopiaprince/micropython,vriera/micropython,blazewicz/micropython,TDAbboud/micropython,pramasoul/micropython,torwag/micropython,mianos/micropython,tuc-osg/micropython,feilongfl/micropython,adafruit/micropython,kerneltask/micropython,HenrikSolver/micropython,blmorris/micropython,orionrobots/micropython,ryannathans/micropython,puuu/micropython,omtinez/micropython,pfalcon/micropython,HenrikSolver/micropython,alex-march/micropython,tuc-osg/micropython,deshipu/micropython,bvernoux/micropython,omtinez/micropython,HenrikSolver/micropython,dhylands/micropython,galenhz/micropython,micropython/micropython-esp32,rubencabrera/micropython,TDAbboud/micropython,paul-xxx/micropython,paul-xxx/micropython,praemdonck/micropython,cloudformdesign/micropython,hosaka/micropython,henriknelson/micropython,galenhz/micropython,jmarcelino/pycom-micropython,galenhz/micropython,EcmaXp/micropython,swegener/micropython,aethaniel/micropython,PappaPeppar/micropython,heisewangluo/micropython,emfcamp/micropython,dmazzella/micropython,mgyenik/micropython,ChuckM/micropython,puuu/micropython,MrSurly/micropython-esp32,methoxid/micropystat,mhoffma/micropython,matthewelse/micropython,kerneltask/micropython,kostyll/micropython,SHA2017-badge/micropython-esp32,praemdonck/micropython,dxxb/micropython,Timmenem/micropython,adafruit/micropython,selste/micropython,rubencabrera/micropython,emfcamp/micropython,selste/micropython,drrk/micropython,pramasoul/micropython,Peetz0r/micropython-esp32,dhylands/micropython,mianos/micropython,ceramos/micropython,aethaniel/micropython,feilongfl/micropython,ahotam/micropython,slzatz/micropython,ceramos/micropython,stonegithubs/micropython,cnoviello/micropython,slzatz/micropython,ericsnowcurrently/micropython,pfalcon/micropython,cloudformdesign/micropython,TDAbboud/micropython,lowRISC/micropython,chrisdearman/micropython,mpalomer/micropython,redbear/micropython,puuu/micropython,orionrobots/micropython,tdautc19841202/micropython,ahotam/micropython,warner83/micropython,adamkh/micropython,neilh10/micropython,KISSMonX/micropython,tuc-osg/micropython,toolmacher/micropython,omtinez/micropython,aitjcize/micropython,pfalcon/micropython,oopy/micropython,supergis/micropython,xhat/micropython,PappaPeppar/micropython,hiway/micropython,jlillest/micropython,vriera/micropython,torwag/micropython,warner83/micropython,adafruit/circuitpython,Peetz0r/micropython-esp32,slzatz/micropython,mhoffma/micropython,EcmaXp/micropython,paul-xxx/micropython,aitjcize/micropython,ernesto-g/micropython,jimkmc/micropython,xyb/micropython,toolmacher/micropython,ericsnowcurrently/micropython,tobbad/micropython,adafruit/micropython,pozetroninc/micropython,xuxiaoxin/micropython,emfcamp/micropython,mgyenik/micropython,bvernoux/micropython,adafruit/micropython,ChuckM/micropython,pramasoul/micropython,lowRISC/micropython,ernesto-g/micropython,redbear/micropython,bvernoux/micropython,heisewangluo/micropython,ericsnowcurrently/micropython,henriknelson/micropython,matthewelse/micropython,martinribelotta/micropython,swegener/micropython,pramasoul/micropython,oopy/micropython,orionrobots/micropython,turbinenreiter/micropython,noahwilliamsson/micropython,puuu/micropython,jimkmc/micropython,martinribelotta/micropython,skybird6672/micropython,toolmacher/micropython,kostyll/micropython,AriZuu/micropython,tobbad/micropython,utopiaprince/micropython,cnoviello/micropython,aethaniel/micropython,deshipu/micropython,aethaniel/micropython,mpalomer/micropython,skybird6672/micropython,ganshun666/micropython,omtinez/micropython,noahwilliamsson/micropython,warner83/micropython,neilh10/micropython,MrSurly/micropython-esp32,drrk/micropython,MrSurly/micropython,tuc-osg/micropython,ceramos/micropython,ahotam/micropython,redbear/micropython,ganshun666/micropython,methoxid/micropystat,ryannathans/micropython,xyb/micropython,galenhz/micropython,SHA2017-badge/micropython-esp32,tdautc19841202/micropython,adafruit/circuitpython,infinnovation/micropython,lowRISC/micropython,oopy/micropython,lbattraw/micropython,trezor/micropython,cwyark/micropython,misterdanb/micropython,MrSurly/micropython,xhat/micropython,AriZuu/micropython,tuc-osg/micropython,dmazzella/micropython,ernesto-g/micropython,hiway/micropython,micropython/micropython-esp32,PappaPeppar/micropython,oopy/micropython,stonegithubs/micropython,pozetroninc/micropython,feilongfl/micropython,warner83/micropython,lbattraw/micropython,cloudformdesign/micropython,suda/micropython,pozetroninc/micropython,xuxiaoxin/micropython,ceramos/micropython,mpalomer/micropython,dinau/micropython,swegener/micropython,chrisdearman/micropython,drrk/micropython,xuxiaoxin/micropython,micropython/micropython-esp32,dxxb/micropython,tralamazza/micropython,misterdanb/micropython,jimkmc/micropython,suda/micropython,mhoffma/micropython,mianos/micropython,emfcamp/micropython,ceramos/micropython,drrk/micropython,stonegithubs/micropython,kerneltask/micropython,danicampora/micropython,swegener/micropython,alex-robbins/micropython,Timmenem/micropython,cloudformdesign/micropython,ernesto-g/micropython,adafruit/circuitpython,suda/micropython,vitiral/micropython,SHA2017-badge/micropython-esp32,ericsnowcurrently/micropython,mhoffma/micropython,cwyark/micropython,dinau/micropython,SungEun-Steve-Kim/test-mp,adamkh/micropython,methoxid/micropystat,slzatz/micropython,chrisdearman/micropython,jlillest/micropython,PappaPeppar/micropython,deshipu/micropython,adamkh/micropython,dhylands/micropython,redbear/micropython,tdautc19841202/micropython,Peetz0r/micropython-esp32,infinnovation/micropython,oopy/micropython,toolmacher/micropython,firstval/micropython,matthewelse/micropython,blazewicz/micropython,hosaka/micropython,Timmenem/micropython,cwyark/micropython,jlillest/micropython,praemdonck/micropython,deshipu/micropython,orionrobots/micropython,xhat/micropython,jlillest/micropython,ganshun666/micropython,danicampora/micropython,lbattraw/micropython,alex-march/micropython,ChuckM/micropython,omtinez/micropython,alex-robbins/micropython,mhoffma/micropython,danicampora/micropython,selste/micropython,TDAbboud/micropython,tobbad/micropython,ahotam/micropython,kostyll/micropython,tobbad/micropython,noahchense/micropython,firstval/micropython,pramasoul/micropython,jmarcelino/pycom-micropython,paul-xxx/micropython,utopiaprince/micropython,adafruit/micropython,xyb/micropython,vriera/micropython,dxxb/micropython,ernesto-g/micropython,mpalomer/micropython,henriknelson/micropython,xuxiaoxin/micropython,lbattraw/micropython,dxxb/micropython,swegener/micropython,aethaniel/micropython,Timmenem/micropython,infinnovation/micropython,turbinenreiter/micropython,adafruit/circuitpython,martinribelotta/micropython,micropython/micropython-esp32,vitiral/micropython,hiway/micropython,firstval/micropython,paul-xxx/micropython,AriZuu/micropython,cnoviello/micropython,Vogtinator/micropython,henriknelson/micropython,SungEun-Steve-Kim/test-mp,drrk/micropython,MrSurly/micropython-esp32,ryannathans/micropython,blazewicz/micropython,ericsnowcurrently/micropython,noahchense/micropython,adamkh/micropython,HenrikSolver/micropython,EcmaXp/micropython,tdautc19841202/micropython,skybird6672/micropython,trezor/micropython,suda/micropython,mianos/micropython,selste/micropython,misterdanb/micropython,trezor/micropython,HenrikSolver/micropython,alex-march/micropython,stonegithubs/micropython,Vogtinator/micropython,micropython/micropython-esp32,kerneltask/micropython,blmorris/micropython,torwag/micropython,puuu/micropython,PappaPeppar/micropython,rubencabrera/micropython,firstval/micropython,redbear/micropython,adafruit/circuitpython,hosaka/micropython,noahchense/micropython,hosaka/micropython,misterdanb/micropython,adafruit/circuitpython,kostyll/micropython,selste/micropython,dhylands/micropython,adamkh/micropython,kostyll/micropython,xyb/micropython,Vogtinator/micropython,dhylands/micropython,ruffy91/micropython,pozetroninc/micropython,xuxiaoxin/micropython,SungEun-Steve-Kim/test-mp,firstval/micropython,ruffy91/micropython,skybird6672/micropython,pfalcon/micropython,alex-robbins/micropython,dmazzella/micropython,hosaka/micropython,vitiral/micropython,supergis/micropython,torwag/micropython,supergis/micropython,jmarcelino/pycom-micropython,alex-march/micropython,ruffy91/micropython,danicampora/micropython,trezor/micropython,alex-robbins/micropython,jimkmc/micropython,jmarcelino/pycom-micropython,torwag/micropython,methoxid/micropystat,chrisdearman/micropython,lowRISC/micropython,noahwilliamsson/micropython,noahchense/micropython,KISSMonX/micropython,galenhz/micropython,EcmaXp/micropython,tralamazza/micropython,AriZuu/micropython,cloudformdesign/micropython,matthewelse/micropython,MrSurly/micropython,jmarcelino/pycom-micropython,kerneltask/micropython,utopiaprince/micropython,Timmenem/micropython,turbinenreiter/micropython,praemdonck/micropython,blazewicz/micropython,aitjcize/micropython,lbattraw/micropython,heisewangluo/micropython,hiway/micropython,skybird6672/micropython,blmorris/micropython,ChuckM/micropython,heisewangluo/micropython,neilh10/micropython,pozetroninc/micropython,supergis/micropython,toolmacher/micropython,cwyark/micropython,utopiaprince/micropython,jlillest/micropython,vriera/micropython,Peetz0r/micropython-esp32,blmorris/micropython,SungEun-Steve-Kim/test-mp,dmazzella/micropython,mgyenik/micropython,ChuckM/micropython,ganshun666/micropython,bvernoux/micropython,tobbad/micropython,tdautc19841202/micropython,AriZuu/micropython,methoxid/micropystat,feilongfl/micropython,hiway/micropython,matthewelse/micropython,dxxb/micropython,ruffy91/micropython,KISSMonX/micropython,EcmaXp/micropython,SungEun-Steve-Kim/test-mp,dinau/micropython,ryannathans/micropython,tralamazza/micropython,KISSMonX/micropython,neilh10/micropython,ganshun666/micropython,deshipu/micropython,bvernoux/micropython,MrSurly/micropython,heisewangluo/micropython,MrSurly/micropython-esp32,blmorris/micropython,slzatz/micropython,cnoviello/micropython,neilh10/micropython,ryannathans/micropython,noahwilliamsson/micropython,feilongfl/micropython,MrSurly/micropython-esp32,alex-march/micropython,pfalcon/micropython,lowRISC/micropython,Vogtinator/micropython,turbinenreiter/micropython,Vogtinator/micropython,ahotam/micropython,vriera/micropython,turbinenreiter/micropython,vitiral/micropython,mianos/micropython