[AsmPrinter] Make AsmPrinter's OutStreamer member a unique_ptr.

AsmPrinter owns the OutStreamer, so an owning pointer makes sense here. Using a
reference for this is crufty.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235752 91177308-0d34-0410-b5e6-96231b3b80d8
37 files changed