swift_build_sdk_interfaces.py: adjust output directory path to an SDK-versioned directory
swift_build_sdk_interfaces.py: adjust output directory path to an SDK-versioned directory

When clients specify an output directory without SDK version, the script will change
the input so we emit all prebuilt module caches into SDK-versioned directories without
modifying the client side.

rdar://67951012

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