Enable 'System.Private.CoreLib.dll' build on cross build mode (#5320)
Enable 'System.Private.CoreLib.dll' build on cross build mode (#5320)

Currently, build.sh uses 'BuildOS' and 'BuildArch' to determine whether
it is possible to build 'System.Private.CorLib.dll'.

This commit revises build.sh to use 'HostOS' and 'HostArch' instead of
'BuildOS' and 'BuildArch' when it checkes whether it is possible to
build 'System.Private.CoreLib.dll', which allows to build
'System.Private.CoreLib.dll' in cross build mode.
bartdesmet/coreclr,manu-silicon/coreclr,KrzysztofCwalina/coreclr,YongseopKim/coreclr,hseok-oh/coreclr,hseok-oh/coreclr,cshung/coreclr,jhendrixMSFT/coreclr,tijoytom/coreclr,russellhadley/coreclr,wateret/coreclr,poizan42/coreclr,ragmani/coreclr,wateret/coreclr,LLITCHEV/coreclr,yizhang82/coreclr,krytarowski/coreclr,Dmitry-Me/coreclr,rartemev/coreclr,cmckinsey/coreclr,AlexGhiondea/coreclr,LLITCHEV/coreclr,ZhichengZhu/coreclr,gkhanna79/coreclr,mmitche/coreclr,mskvortsov/coreclr,AlexGhiondea/coreclr,sjsinju/coreclr,krk/coreclr,botaberg/coreclr,krk/coreclr,krytarowski/coreclr,cydhaselton/coreclr,cmckinsey/coreclr,Dmitry-Me/coreclr,botaberg/coreclr,JosephTremoulet/coreclr,bartdesmet/coreclr,dasMulli/coreclr,James-Ko/coreclr,kyulee1/coreclr,ramarag/coreclr,sagood/coreclr,Dmitry-Me/coreclr,AlexGhiondea/coreclr,hseok-oh/coreclr,tijoytom/coreclr,tijoytom/coreclr,parjong/coreclr,naamunds/coreclr,AlexGhiondea/coreclr,AlexGhiondea/coreclr,pgavlin/coreclr,ragmani/coreclr,shahid-pk/coreclr,dpodder/coreclr,shahid-pk/coreclr,James-Ko/coreclr,bartdesmet/coreclr,mskvortsov/coreclr,ruben-ayrapetyan/coreclr,cydhaselton/coreclr,wateret/coreclr,shahid-pk/coreclr,rartemev/coreclr,jhendrixMSFT/coreclr,manu-silicon/coreclr,alexperovich/coreclr,James-Ko/coreclr,manu-silicon/coreclr,krk/coreclr,James-Ko/coreclr,sagood/coreclr,jamesqo/coreclr,qiudesong/coreclr,bartdesmet/coreclr,russellhadley/coreclr,ramarag/coreclr,qiudesong/coreclr,hseok-oh/coreclr,JosephTremoulet/coreclr,dasMulli/coreclr,poizan42/coreclr,neurospeech/coreclr,schellap/coreclr,yizhang82/coreclr,alexperovich/coreclr,pgavlin/coreclr,vinnyrom/coreclr,wateret/coreclr,yeaicc/coreclr,mskvortsov/coreclr,JonHanna/coreclr,LLITCHEV/coreclr,krytarowski/coreclr,KrzysztofCwalina/coreclr,sjsinju/coreclr,ramarag/coreclr,martinwoodward/coreclr,dasMulli/coreclr,sjsinju/coreclr,cmckinsey/coreclr,roncain/coreclr,pgavlin/coreclr,ZhichengZhu/coreclr,gkhanna79/coreclr,qiudesong/coreclr,schellap/coreclr,naamunds/coreclr,cshung/coreclr,roncain/coreclr,jamesqo/coreclr,schellap/coreclr,gkhanna79/coreclr,cydhaselton/coreclr,cshung/coreclr,naamunds/coreclr,yeaicc/coreclr,mmitche/coreclr,yeaicc/coreclr,jhendrixMSFT/coreclr,manu-silicon/coreclr,jhendrixMSFT/coreclr,ZhichengZhu/coreclr,James-Ko/coreclr,naamunds/coreclr,JosephTremoulet/coreclr,ruben-ayrapetyan/coreclr,josteink/coreclr,mskvortsov/coreclr,wateret/coreclr,naamunds/coreclr,cshung/coreclr,manu-silicon/coreclr,qiudesong/coreclr,jamesqo/coreclr,ZhichengZhu/coreclr,YongseopKim/coreclr,poizan42/coreclr,manu-silicon/coreclr,ZhichengZhu/coreclr,russellhadley/coreclr,cshung/coreclr,sagood/coreclr,LLITCHEV/coreclr,neurospeech/coreclr,jamesqo/coreclr,cmckinsey/coreclr,vinnyrom/coreclr,rartemev/coreclr,poizan42/coreclr,dpodder/coreclr,botaberg/coreclr,roncain/coreclr,manu-silicon/coreclr,ramarag/coreclr,mmitche/coreclr,kyulee1/coreclr,jhendrixMSFT/coreclr,wateret/coreclr,mskvortsov/coreclr,tijoytom/coreclr,gkhanna79/coreclr,cshung/coreclr,parjong/coreclr,pgavlin/coreclr,shahid-pk/coreclr,vinnyrom/coreclr,sjsinju/coreclr,naamunds/coreclr,alexperovich/coreclr,russellhadley/coreclr,wtgodbe/coreclr,martinwoodward/coreclr,parjong/coreclr,kyulee1/coreclr,tijoytom/coreclr,hseok-oh/coreclr,wtgodbe/coreclr,mmitche/coreclr,sagood/coreclr,rartemev/coreclr,tijoytom/coreclr,schellap/coreclr,KrzysztofCwalina/coreclr,schellap/coreclr,James-Ko/coreclr,ZhichengZhu/coreclr,bartdesmet/coreclr,YongseopKim/coreclr,poizan42/coreclr,ruben-ayrapetyan/coreclr,sagood/coreclr,dpodder/coreclr,neurospeech/coreclr,martinwoodward/coreclr,yizhang82/coreclr,martinwoodward/coreclr,krk/coreclr,pgavlin/coreclr,josteink/coreclr,cmckinsey/coreclr,ragmani/coreclr,KrzysztofCwalina/coreclr,naamunds/coreclr,martinwoodward/coreclr,Dmitry-Me/coreclr,ruben-ayrapetyan/coreclr,JosephTremoulet/coreclr,neurospeech/coreclr,parjong/coreclr,krytarowski/coreclr,martinwoodward/coreclr,botaberg/coreclr,JonHanna/coreclr,rartemev/coreclr,roncain/coreclr,ramarag/coreclr,wtgodbe/coreclr,vinnyrom/coreclr,sjsinju/coreclr,alexperovich/coreclr,YongseopKim/coreclr,russellhadley/coreclr,dpodder/coreclr,ramarag/coreclr,parjong/coreclr,cydhaselton/coreclr,kyulee1/coreclr,krk/coreclr,KrzysztofCwalina/coreclr,vinnyrom/coreclr,jamesqo/coreclr,parjong/coreclr,botaberg/coreclr,dpodder/coreclr,AlexGhiondea/coreclr,kyulee1/coreclr,shahid-pk/coreclr,dasMulli/coreclr,cydhaselton/coreclr,bartdesmet/coreclr,gkhanna79/coreclr,martinwoodward/coreclr,Dmitry-Me/coreclr,JonHanna/coreclr,neurospeech/coreclr,bartdesmet/coreclr,KrzysztofCwalina/coreclr,yizhang82/coreclr,rartemev/coreclr,shahid-pk/coreclr,JosephTremoulet/coreclr,sagood/coreclr,yizhang82/coreclr,LLITCHEV/coreclr,jamesqo/coreclr,botaberg/coreclr,ZhichengZhu/coreclr,qiudesong/coreclr,JonHanna/coreclr,yeaicc/coreclr,schellap/coreclr,alexperovich/coreclr,vinnyrom/coreclr,jhendrixMSFT/coreclr,sjsinju/coreclr,yeaicc/coreclr,krytarowski/coreclr,cmckinsey/coreclr,roncain/coreclr,josteink/coreclr,dasMulli/coreclr,YongseopKim/coreclr,ramarag/coreclr,roncain/coreclr,jhendrixMSFT/c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