isn't ideal if we want to be able to use another object file format.
Add a createObjectStreamer() factory method so that the correct object
file streamer can be instantiated for a given target triple.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104318 91177308-0d34-0410-b5e6-96231b3b80d8