[tlbuild] Mingw64 build using MSYS2 environment

[Angelo Graziosi]

I wonder if you are going to add an x86_64 mingw64 build to future TL 
releases.

MSYS2 is a linux-like environment (technically, a fork from Cygwin) 
which aims to build Windows native apps (see: 
http://sourceforge.net/p/msys2/wiki/Home)

Many Windows apps have been built using this way (see: 
http://sourceforge.net/p/msys2/wiki/Packages)

That port for TeXLive would be very interesting.


  Angelo