* Make contained ostream pointer, not reference
* Allow setting of that ostream via setStream()
class CachedWriter:
* setStream() in turn calls setStream() on the AssemblyWriter
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13247 91177308-0d34-0410-b5e6-96231b3b80d8