[SCEV] Make it obvious BackedgeTakenInfo's constructor steals storage

Specifically, it moves SCEVUnionPredicates from its input into its own
storage.  Make this obvious at the type level.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282374 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed