[build-script-impl] Handle multiple version directories in TOOLCHAIN/usr/lib/clang.
[build-script-impl] Handle multiple version directories in TOOLCHAIN/usr/lib/clang.

This ensures that compiler-rt gets copied across even if there's more than one version listed.

rdar://problem/55974236
aschwaighofer/swift,harlanhaskins/swift,jmgc/swift,karwa/swift,nathawes/swift,allevato/swift,jmgc/swift,benlangmuir/swift,jmgc/swift,JGiola/swift,airspeedswift/swift,lorentey/swift,CodaFi/swift,JGiola/swift,roambotics/swift,hooman/swift,parkera/swift,benlangmuir/swift,lorentey/swift,lorentey/swift,nathawes/swift,gribozavr/swift,hooman/swift,karwa/swift,gregomni/swift,gribozavr/swift,xwu/swift,gregomni/swift,stephentyrone/swift,parkera/swift,parkera/swift,airspeedswift/swift,gribozavr/swift,jckarter/swift,atrick/swift,benlangmuir/swift,karwa/swift,tkremenek/swift,devincoughlin/swift,tkremenek/swift,devincoughlin/swift,jmgc/swift,gribozavr/swift,apple/swift,lorentey/swift,rudkx/swift,jmgc/swift,nathawes/swift,karwa/swift,CodaFi/swift,airspeedswift/swift,gribozavr/swift,devincoughlin/swift,nathawes/swift,stephentyrone/swift,harlanhaskins/swift,stephentyrone/swift,roambotics/swift,gribozavr/swift,roambotics/swift,parkera/swift,harlanhaskins/swift,tkremenek/swift,parkera/swift,lorentey/swift,ahoppen/swift,devincoughlin/swift,karwa/swift,devincoughlin/swift,glessard/swift,allevato/swift,gregomni/swift,stephentyrone/swift,ahoppen/swift,lorentey/swift,rudkx/swift,allevato/swift,glessard/swift,airspeedswift/swift,jckarter/swift,rudkx/swift,airspeedswift/swift,benlangmuir/swift,harlanhaskins/swift,harlanhaskins/swift,ahoppen/swift,harlanhaskins/swift,allevato/swift,xwu/swift,apple/swift,jckarter/swift,parkera/swift,roambotics/swift,xwu/swift,allevato/swift,harlanhaskins/swift,aschwaighofer/swift,glessard/swift,hooman/swift,nathawes/swift,stephentyrone/swift,gregomni/swift,aschwaighofer/swift,tkremenek/swift,parkera/swift,atrick/swift,apple/swift,devincoughlin/swift,CodaFi/swift,karwa/swift,ahoppen/swift,nathawes/swift,xwu/swift,aschwaighofer/swift,stephentyrone/swift,ahoppen/swift,allevato/swift,atrick/swift,gregomni/swift,apple/swift,rudkx/swift,jmgc/swift,airspeedswift/swift,atrick/swift,hooman/swift,benlangmuir/swift,xwu/swift,rudkx/swift,lorentey/swift,benlangmuir/swift,glessard/swift,jckarter/swift,glessard/swift,allevato/swift,parkera/swift,aschwaighofer/swift,JGiola/swift,roambotics/swift,tkremenek/swift,gribozavr/swift,devincoughlin/swift,rudkx/swift,CodaFi/swift,apple/swift,stephentyrone/swift,airspeedswift/swift,hooman/swift,gregomni/swift,ahoppen/swift,atrick/swift,devincoughlin/swift,jckarter/swift,karwa/swift,karwa/swift,jckarter/swift,hooman/swift,JGiola/swift,apple/swift,jmgc/swift,jckarter/swift,tkremenek/swift,atrick/swift,xwu/swift,aschwaighofer/swift,lorentey/swift,CodaFi/swift,gribozavr/swift,roambotics/swift,JGiola/swift,xwu/swift,aschwaighofer/swift,tkremenek/swift,JGiola/swift,nathawes/swift,glessard/swift,hooman/swift,CodaFi/swift,CodaFi/swift