Make tool_output_file's raw_ostream instance a member variable instead

Make tool_output_file's raw_ostream instance a member variable instead
of a base class.

This makes it possible to unregister the file from FilesToRemove when
the file is done. Also, this eliminates the need for
formatted_tool_output_file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112706 91177308-0d34-0410-b5e6-96231b3b80d8