[PATCH] Add writeFileWithSystemEncoding to LibLLVMSupport

[Rafael Espíndola]

> I also refactored part of the write function in raw_fd_ostream out of this class, to avoid duplicating code in this implementation.

Yes, this class is way too central to get an extra feature just for
response files.

You can maybe add a new streamer class, but I must say I am not sure
it is worth it. Response files are relatively small, so I would
probably start with what you had before: build a buffer and then dump
it. This also avoids having to handle incomplete characters
(getIncompleteUTFBytes)

Cheers,
Rafael