[PATCH] D28010: FileOutputBuffer: support non-mmap'able file.

[Rafael Avila de Espindola via llvm-commits]

> +// Represents a non-memory-mapped file. We need this class
> +// because not all files are mmap'able. For example, /dev/null
> +// is not mmap'able.

The comment is a bit confusing. The issue is that with the old code if
you tried to "-o /dev/null", we would not try to mmap /dev/null. We
would try to mmap a temp file and move it to /dev/null.

Maybe the best way to do this is
* Check the file type as you did.
* Remember the result in a member variable.
* If it is regular, use fs::createUniqueFile.
* If it is not, use fs::createTemporaryFile, which can also be mmaped.
* In commit, do a move if the target is regular or write the contents if
  it is not.

That should reduce the code difference between the two cases.

Cheers,
Rafael