mingw: implement syslog

mingw: implement syslog

Syslog does not usually exist on Windows, so implement our own using
Window's ReportEvent mechanism.

Strings containing "%1" gets expanded into them selves by ReportEvent,
resulting in an unreadable string. "%2" and above is not a problem.
Unfortunately, on Windows an IPv6 address can contain "%1", so expand
"%1" to "% 1" before reporting. "%%1" is also a problem for ReportEvent,
but that string cannot occur in an IPv6 address.

Signed-off-by: Mike Pape <dotzenlabs@gmail.com>
Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>