cmMessenger: Revert to non-color messages on Windows
Since !6105 (merged) the message output no longer goes
through our custom streambuf on Windows that converts output encoding.
This can cause messages to be printed with the wrong encoding in a
Windows Console. It also causes messages to have a mix of LF and CRLF
stderr converts LF to CRLF but our custom streambuf
Revert to using just
cerr for messages on Windows. Another approach
will be needed to achieve color output on Windows later.