Fix call to `collectUsedGlobalVariables`
Fix call to `collectUsedGlobalVariables`

LLVM commit 3adb89bb9f8e73c82787babb2f877fece7394770 updated the API of
this function to take a reference to a `SmallVectorImpl` instead of a
set to ensure that it behaves deterministically.

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