constructed with an output filename of "-". In particular, allow the
file descriptor to be closed, and close the file descriptor in the
destructor if it hasn't been explicitly closed already, to ensure
that any write errors are detected.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111436 91177308-0d34-0410-b5e6-96231b3b80d8
