Revert "Infer a reasonable build subdirectory when building a toolchain"
Revert "Infer a reasonable build subdirectory when building a toolchain"

This reverts commit 73a135307ed198fb44ccd5da0c5801aee09232ea.

xwu/swift,gregomni/swift,benlangmuir/swift,rudkx/swift,rudkx/swift,apple/swift,benlangmuir/swift,glessard/swift,gregomni/swift,apple/swift,JGiola/swift,ahoppen/swift,roambotics/swift,gregomni/swift,roambotics/swift,atrick/swift,xwu/swift,apple/swift,roambotics/swift,apple/swift,ahoppen/swift,atrick/swift,rudkx/swift,JGiola/swift,xwu/swift,JGiola/swift,glessard/swift,roambotics/swift,JGiola/swift,glessard/swift,ahoppen/swift,rudkx/swift,roambotics/swift,gregomni/swift,xwu/swift,xwu/swift,ahoppen/swift,JGiola/swift,xwu/swift,benlangmuir/swift,glessard/swift,benlangmuir/swift,atrick/swift,rudkx/swift,ahoppen/swift,xwu/swift,atrick/swift,ahoppen/swift,rudkx/swift,benlangmuir/swift,gregomni/swift,apple/swift,glessard/swift,atrick/swift,benlangmuir/swift,roambotics/swift,apple/swift,JGiola/swift,gregomni/swift,glessard/swift,atrick/swift