[build] extend support for building with a prebuilt toolchain to the corelibs and llbuild
[build] extend support for building with a prebuilt toolchain to the corelibs and llbuild

apple/swift,xwu/swift,nathawes/swift,roambotics/swift,jckarter/swift,parkera/swift,apple/swift,JGiola/swift,xwu/swift,glessard/swift,rudkx/swift,roambotics/swift,glessard/swift,benlangmuir/swift,atrick/swift,rudkx/swift,xwu/swift,hooman/swift,jckarter/swift,hooman/swift,ahoppen/swift,airspeedswift/swift,roambotics/swift,CodaFi/swift,airspeedswift/swift,hooman/swift,atrick/swift,jckarter/swift,apple/swift,gregomni/swift,glessard/swift,jckarter/swift,JGiola/swift,parkera/swift,rudkx/swift,airspeedswift/swift,rudkx/swift,gregomni/swift,gregomni/swift,allevato/swift,glessard/swift,jmgc/swift,tkremenek/swift,allevato/swift,gregomni/swift,airspeedswift/swift,tkremenek/swift,roambotics/swift,CodaFi/swift,apple/swift,parkera/swift,nathawes/swift,xwu/swift,jmgc/swift,CodaFi/swift,airspeedswift/swift,atrick/swift,CodaFi/swift,hooman/swift,ahoppen/swift,benlangmuir/swift,apple/swift,xwu/swift,nathawes/swift,allevato/swift,ahoppen/swift,jmgc/swift,benlangmuir/swift,jckarter/swift,parkera/swift,jckarter/swift,xwu/swift,parkera/swift,rudkx/swift,allevato/swift,atrick/swift,atrick/swift,tkremenek/swift,ahoppen/swift,jmgc/swift,nathawes/swift,jckarter/swift,allevato/swift,roambotics/swift,nathawes/swift,xwu/swift,jmgc/swift,tkremenek/swift,airspeedswift/swift,allevato/swift,hooman/swift,tkremenek/swift,apple/swift,roambotics/swift,gregomni/swift,benlangmuir/swift,JGiola/swift,CodaFi/swift,glessard/swift,tkremenek/swift,rudkx/swift,hooman/swift,airspeedswift/swift,parkera/swift,gregomni/swift,allevato/swift,ahoppen/swift,atrick/swift,benlangmuir/swift,CodaFi/swift,nathawes/swift,JGiola/swift,benlangmuir/swift,parkera/swift,jmgc/swift,hooman/swift,ahoppen/swift,parkera/swift,JGiola/swift,JGiola/swift,tkremenek/swift,CodaFi/swift,jmgc/swift,nathawes/swift,glessard/swift