[Mingw-cross-env-list] jpeg should be replaced by libjpeg-turbo

[Nikos Chantziaras]

Although it would appear that the jpeg library from ijg.org is the 
standard, many people, including the many Linux distributions, use 
libjpeg-turbo instead.  I think MXE should use it too:

http://libjpeg-turbo.virtualgl.org

It's a drop-in replacement for jpeg.