Support outputting to /dev/null.

Support outputting to /dev/null.

When writing to a non regular file we cannot rename to it. Since we
have to write, we may as well create a temporary file to avoid trying
to create an unique file in /dev when trying to write to /dev/null.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291485 91177308-0d34-0410-b5e6-96231b3b80d8