formatted_raw_ostream both is-a raw_ostream and has-a raw_ostream. This

formatted_raw_ostream both is-a raw_ostream and has-a raw_ostream. This
means that two separate raw_ostreams are doing buffering before data is
sent to the underlying stream. Besides the inefficiency of redundant
buffering, the second level of buffering doesn't recieve flush()
requests.

Fix this by having formatted_raw_ostream set the underlying raw_ostream
to be unbuffered. This eliminates inefficiency due to redundant buffering,
and it makes the flush() disconnect harmless.

This fixes PR4559.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75883 91177308-0d34-0410-b5e6-96231b3b80d8