unique_ptrify ConsumedBlockInfo analysis to make it move assignable

ConsumedBlockInfo objects were move assigned, but only in a state where
the dtor was a no-op anyway. Subtle and easily could've happened in ways
that wouldn't've been safe - so this change makes it safe no matter what
state the ConsumedBlockInfo object is in.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@244998 91177308-0d34-0410-b5e6-96231b3b80d8