Improve error messages during build.
Improve error messages during build.

gasolin/blockly,drigz/blockly,carlosperate/ardublockly,caiograg/blockly,MikeDX/blockly-div,ChinJY/blockly,g-rocket/blockly,Immortalin/blockly,rdelhommer/BlocklyPrototypeEB,xeecos/blockly,nickmain/blockly,mark-friedman/blockly,ominux/blockly,sclements/scratch-blocks,InspectorWidget/blockly,gudtago/blockly,carloslfu/blockly,gabrielsanchez/blockly,nickmain/blockly,mark-friedman/blockly,marianoguerra/blockly,aseba-community/blockly,gengshenghong/scratch-blocks,rachel-fenichel/blockly,ymnk13/blockly,rasata/blockly,UIKit0/blockly,ymnk13/blockly,LLK/scratch-blocks,rachel-fenichel/blockly,Jhara/blockly,google/blockly,shabesoglu/blockly,caiograg/blockly,OpenRoberta/blockly,ensonic/blockly,carlosperate/blockly,gupta137/blockly,EmergingTechnologyAdvisors/blockly,ymnk13/blockly,faizshukri/blockly,markocelan/blockly-minecraft,stefan-j/blockly,aseba-community/blockly,trodi/blockly,HALtheWise/blockly,groklearning/blockly,ralic/blockly,LLK/scratch-blocks,thr0w/blockly,yhbest/blockly,sclements/scratch-blocks,Jhara/blockly,aravart/speech-blocks,jstnhuang/blockly,charlynz/blockly-adventure,thekoalaz/blockly,SheldonPacotti/blockly-enhancements,shyamalschandra/blockly,aravart/speech-blocks,nickmain/blockly,griffpatch/scratch-blocks,edbutler/blockly,rachel-fenichel/blockly,hybrideagle/blockly,adrgerez/ardublockly,touqir14/blockly,jstnhuang/blockly,joshlory/blockly,smalruby/blockly,cdjackson/openhab-blockly,MoziSong/blockly_dyn_devices,caiograg/blockly,edbutler/blockly,trodi/blockly,thekoalaz/blockly,Kaworru/blockly,lzairdking/blockly,griffpatch/scratch-blocks,Gamefroot/Gamefroot-Blockly,daarond/blockly,shabesoglu/blockly,mehrdadrafiee/blockly,yhbest/blockly,nickmain/blockly,jano42/blockly,gudtago/blockly,andersschuller/blockly,gengshenghong/scratch-blocks,sclements/scratch-blocks,google/blockly,rachel-fenichel/blockly,eclecticdave/blockly,sonwh98/blockly,MikeDX/blockly-div,lzairdking/blockly,rasata/blockly,EinsteinsWorkshop/blockly,joshlory/blockly,rachel-fenichel/blockly,ylixir/blockly,OpenRoberta/blockly,RealTimeWeb/blockpy,jisqyv/blockly,carlosperate/blockly,daarond/blockly,ocadotechnology/blockly,dhalupa/blockly,josmas/blockly,markocelan/blockly-minecraft,dhalupa/blockly,g-rocket/blockly,drigz/blockly,groklearning/blockly,drigz/blockly,Program-AR/blockly,google/blockly-devtools,g-rocket/blockly,google/blockly,michalkilawok/blockly,google/blockly,UIKit0/blockly,Andrews9008/blockly,orionhealth/blockly,hkoi/blockly,kingoo/blockly,UIKit0/blockly,picklesrus/blockly,MaryS94/blockly,krahman/blockly,trinketapp/blockly,ralic/blockly,jstnhuang/blockly,trinketapp/blockly,michalkilawok/blockly,in1004kyu/tokitool,jordicamposmiralles/geoblockly,InspectorWidget/blockly,HALtheWise/blockly,twodee/blockly,faizshukri/blockly,Kaworru/blockly,sclements/scratch-blocks,shabesoglu/blockly,google/blockly,gasolin/blockly,charlynz/blockly-adventure,stefan-j/blockly,ominux/blockly,aninternetof/blockly,zerar/blockly,cdjackson/openhab-blockly,carloslfu/blockly,MaryS94/blockly,wakashige/blockly,hkoi/blockly,moskalevkirll/blockly,carlosperate/blockly,3agv2004/Programming,prappo/blockly,OpenRoberta/blockly,EinsteinsWorkshop/blockly,marianoguerra/blockly,eclecticdave/blockly,MoziSong/blockly_dyn_devices,paulweatherby/blockly,touqir14/blockly,daarond/blockly,xeecos/blockly,twodee/blockly,josmas/blockly,rasata/blockly,aseba-community/blockly,Immortalin/blockly,hkoi/blockly,Jhara/blockly,CocoMake7/CocoBlockly,Grahack/blockly,hybrideagle/blockly,twodee/blockly,mehrdadrafiee/blockly,mark-friedman/blockly,Gamefroot/Gamefroot-Blockly,paulweatherby/blockly,SheldonPacotti/blockly-enhancements,markocelan/blockly-minecraft,twodee/blockly,stefan-j/blockly,joshlory/blockly,ChinJY/blockly,trodi/blockly,nickmain/blockly,CocoMake7/CocoBlockly,LLK/scratch-blocks,TechplexEngineer/blockly,RealTimeWeb/blockly,gudtago/blockly,altereagle/blockly,vinay5jan/blocklyExtended,griffpatch/scratch-blocks,Program-AR/blockly,Gamefroot/Gamefroot-Blockly,picklesrus/blockly,Tinkerforge/tvpl-blockly,ChinJY/blockly,gengshenghong/scratch-blocks,3agv2004/Programming,sclements/scratch-blocks,MikeDX/blockly-div,cdjackson/openhab-blockly,simpleverso/blockly,altereagle/blockly,lzairdking/blockly,stefan-j/blockly,ensonic/blockly,JackBDu/blockly,MoziSong/blockly_dyn_devices,mark-friedman/blockly,lzairdking/blockly,cmillani/blockly,jisqyv/blockly,ocadotechnology/blockly,InspectorWidget/blockly,toebes-extreme/blockly,groklearning/blockly,griffpatch/scratch-blocks,shyamalschandra/blockly,jano42/blockly,ocadotechnology/blockly,carloslfu/blockly,kingoo/blockly,SheldonPacotti/blockly-enhancements,thr0w/blockly,google/blockly,jstnhuang/blockly,gupta137/blockly,Gamefroot/Gamefroot-Blockly,orionhealth/blockly,smalruby/blockly,sonwh98/blockly,andersschuller/blockly,RealTimeWeb/blockly,in1004kyu/tokitool,carlosperate/ardublockly,Program-AR/blockly,gengshenghong/scratch-blocks,altereagle/blockly,toebes-extreme/blockly,thr0w/blockly,gengshenghong/scratch-blocks,simpleverso/blockly,JackBDu/blockly,rdelhommer/BlocklyPrototypeEB,edbutler/blockly,faizshukri/blockly,EmergingTechnologyAdvisors/blockly,google/blockly,LLK/scratch-blocks,Andrews9008/blockly,eclecticdave/blockly,yhbest/blockly,xeecos/blockly,moskalevkirll/blockly,toebes-extreme/blockly,twodee/blockly,twodee/blockly,jordicamposmiralles/geoblockly,HALtheWise/blockly,Grahack/blockly,picklesrus/blockly,orionhealth/blockly,prappo/blockly,vinay5jan/blocklyExtended,google/blockly-devtools,moskalevkirll/blockly,josmas/blockly,dhalupa/blockly,andersschuller/blockly,griffpatch/scratch-blocks,MaryS94/blockly,Immortalin/blockly,in1004kyu/tokitool,mark-friedman/blockly,JackBDu/blockly,ylixir/blockly,RealTimeWeb/blockpy,gabrielsanchez/blockly,Kaworru/blockly,RealTimeWeb/blockly,ylixir/blockly,LLK/scratch-blocks,RealTimeWeb/blockpy,ralic/blockly,cmillani/blockly,ensonic/blockly,mark-friedman/blockly,zerar/blockly,shyamalschandra/blockly,kingoo/blockly,trodi/blockly,markocelan/blockly-minecraft,simpleverso/blockly,zerar/blockly,krahman/blockly,marianoguerra/blockly,vinay5jan/blocklyExtended,jano42/blockly,rachel-fenichel/blockly,trinketapp/blockly,carlosperate/blockly,ominux/blockly,hybrideagle/blockly,adrgerez/ardublockly,michalkilawok/blockly,Andrews9008/blockly,EinsteinsWorkshop/blockly,aninternetof/blockly,Grahack/blockly,EmergingTechnologyAdvisors/blockly,OpenRoberta/blockly,rachel-fenichel/blockly,3agv2004/Programming,touqir14/blockly,prappo/blockly,nickmain/blockly,gabrielsanchez/blockly,trinketapp/blockly,Tinkerforge/tvpl-blockly,jordicamposmiralles/geoblockly,wakashige/blockly,aninternetof/blockly,CocoMake7/CocoBlockly,TechplexEngineer/blockly,sonwh98/blockly,jisqyv/blockly,thekoalaz/blockly,cmillani/blockly,carlosperate/ardublockly,gupta137/blockly,adrgerez/ardublockly,wakashige/blockly,paulweatherby/blockly,gasolin/blockly,jano42/blockly,groklearning/blockly,Tinkerforge/tvpl-blockly