Revert "Move bootstrap build to MSBuild 14.0"
Revert "Move bootstrap build to MSBuild 14.0"

This reverts commit bb028972e85509af1914c571b2ae6ffcfaff807f.

AlekseyTs/roslyn,kelltrick/roslyn,robinsedlaczek/roslyn,orthoxerox/roslyn,tmeschter/roslyn,physhi/roslyn,reaction1989/roslyn,OmarTawfik/roslyn,diryboy/roslyn,cston/roslyn,diryboy/roslyn,aelij/roslyn,TyOverby/roslyn,KevinH-MS/roslyn,bartdesmet/roslyn,mattwar/roslyn,srivatsn/roslyn,gafter/roslyn,mattscheffer/roslyn,mattwar/roslyn,zooba/roslyn,yeaicc/roslyn,pdelvo/roslyn,wvdd007/roslyn,bbarry/roslyn,amcasey/roslyn,wvdd007/roslyn,a-ctor/roslyn,dotnet/roslyn,jamesqo/roslyn,Giftednewt/roslyn,AmadeusW/roslyn,stephentoub/roslyn,khyperia/roslyn,bkoelman/roslyn,jkotas/roslyn,dpoeschl/roslyn,mavasani/roslyn,MattWindsor91/roslyn,mattscheffer/roslyn,drognanar/roslyn,jcouv/roslyn,dpoeschl/roslyn,vslsnap/roslyn,dotnet/roslyn,Hosch250/roslyn,stephentoub/roslyn,AlekseyTs/roslyn,TyOverby/roslyn,bartdesmet/roslyn,eriawan/roslyn,CyrusNajmabadi/roslyn,Hosch250/roslyn,mmitche/roslyn,AdamSpeight2008/roslyn-AdamSpeight2008,AnthonyDGreen/roslyn,mgoertz-msft/roslyn,jasonmalinowski/roslyn,mattscheffer/roslyn,srivatsn/roslyn,lorcanmooney/roslyn,tannergooding/roslyn,tmat/roslyn,jasonmalinowski/roslyn,xasx/roslyn,swaroop-sridhar/roslyn,CyrusNajmabadi/roslyn,ErikSchierboom/roslyn,DustinCampbell/roslyn,nguerrera/roslyn,mgoertz-msft/roslyn,KirillOsenkov/roslyn,robinsedlaczek/roslyn,akrisiun/roslyn,paulvanbrenk/roslyn,MichalStrehovsky/roslyn,weltkante/roslyn,akrisiun/roslyn,tannergooding/roslyn,tmeschter/roslyn,dotnet/roslyn,panopticoncentral/roslyn,agocke/roslyn,DustinCampbell/roslyn,genlu/roslyn,AdamSpeight2008/roslyn-AdamSpeight2008,AdamSpeight2008/roslyn-AdamSpeight2008,srivatsn/roslyn,mgoertz-msft/roslyn,jmarolf/roslyn,diryboy/roslyn,bkoelman/roslyn,jeffanders/roslyn,KevinRansom/roslyn,akrisiun/roslyn,a-ctor/roslyn,heejaechang/roslyn,physhi/roslyn,jamesqo/roslyn,gafter/roslyn,mavasani/roslyn,amcasey/roslyn,zooba/roslyn,tvand7093/roslyn,Giftednewt/roslyn,MichalStrehovsky/roslyn,xoofx/roslyn,jamesqo/roslyn,genlu/roslyn,MattWindsor91/roslyn,jkotas/roslyn,zooba/roslyn,AArnott/roslyn,xoofx/roslyn,cston/roslyn,davkean/roslyn,heejaechang/roslyn,VSadov/roslyn,brettfo/roslyn,davkean/roslyn,jasonmalinowski/roslyn,ErikSchierboom/roslyn,weltkante/roslyn,xasx/roslyn,swaroop-sridhar/roslyn,bartdesmet/roslyn,xasx/roslyn,mavasani/roslyn,AnthonyDGreen/roslyn,orthoxerox/roslyn,jeffanders/roslyn,KevinRansom/roslyn,orthoxerox/roslyn,MattWindsor91/roslyn,jcouv/roslyn,jcouv/roslyn,reaction1989/roslyn,OmarTawfik/roslyn,KevinH-MS/roslyn,eriawan/roslyn,cston/roslyn,robinsedlaczek/roslyn,CaptainHayashi/roslyn,agocke/roslyn,kelltrick/roslyn,jkotas/roslyn,CaptainHayashi/roslyn,MichalStrehovsky/roslyn,panopticoncentral/roslyn,mmitche/roslyn,aelij/roslyn,bkoelman/roslyn,CyrusNajmabadi/roslyn,tmeschter/roslyn,tvand7093/roslyn,xoofx/roslyn,VSadov/roslyn,stephentoub/roslyn,KirillOsenkov/roslyn,mattwar/roslyn,shyamnamboodiripad/roslyn,brettfo/roslyn,tannergooding/roslyn,pdelvo/roslyn,jmarolf/roslyn,sharwell/roslyn,sharwell/roslyn,kelltrick/roslyn,gafter/roslyn,aelij/roslyn,panopticoncentral/roslyn,yeaicc/roslyn,AmadeusW/roslyn,AmadeusW/roslyn,mmitche/roslyn,swaroop-sridhar/roslyn,khyperia/roslyn,lorcanmooney/roslyn,tmat/roslyn,bbarry/roslyn,weltkante/roslyn,eriawan/roslyn,reaction1989/roslyn,lorcanmooney/roslyn,AArnott/roslyn,dpoeschl/roslyn,wvdd007/roslyn,jeffanders/roslyn,abock/roslyn,KirillOsenkov/roslyn,abock/roslyn,ErikSchierboom/roslyn,AnthonyDGreen/roslyn,AArnott/roslyn,pdelvo/roslyn,tmat/roslyn,davkean/roslyn,AlekseyTs/roslyn,shyamnamboodiripad/roslyn,agocke/roslyn,drognanar/roslyn,Giftednewt/roslyn,tvand7093/roslyn,MattWindsor91/roslyn,paulvanbrenk/roslyn,nguerrera/roslyn,abock/roslyn,OmarTawfik/roslyn,nguerrera/roslyn,a-ctor/roslyn,vslsnap/roslyn,amcasey/roslyn,shyamnamboodiripad/roslyn,jmarolf/roslyn,TyOverby/roslyn,KevinRansom/roslyn,brettfo/roslyn,vslsnap/roslyn,VSadov/roslyn,CaptainHayashi/roslyn,paulvanbrenk/roslyn,khyperia/roslyn,Hosch250/roslyn,KevinH-MS/roslyn,sharwell/roslyn,yeaicc/roslyn,physhi/roslyn,DustinCampbell/roslyn,drognanar/roslyn,heejaechang/roslyn,bbarry/roslyn,genlu/roslyn