esp8266: Make default ESP_SDK variable work correctly.
esp8266: Make default ESP_SDK variable work correctly.

When esp-open-sdk is built with STANDALONE=y (the default) then ESP_SDK
is set to the correct value, so that "make" just works.

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