Add an mgwport file for mingw32-tk

This is based on:

http://cygwin-ports.git.sourceforge.net/git/gitweb.cgi?p=cygwin-ports/mingw-tk;a=blob;f=mingw-tk.cygport;hb=HEAD

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
fixup! mingw32-tcl: Upgrade to version 8.5.12