Add Code Compare v2.80.4 as a merge / diff tool for Windows

Add Code Compare v2.80.4 as a merge / diff tool for Windows

Code Compare is a commercial file comparison tool for Windows, see

    http://www.devart.com/codecompare/

Version 2.80.4 added support for command line arguments preceded by a
dash instead of a slash. This is required for Git for Windows because
slashes in command line arguments get mangled with according to these
rules:

    http://www.mingw.org/wiki/Posix_path_conversion

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>