Added clang support for Windows

I've added a script to build cocos2d-x with clang on windows through mingw64.

I had to enable thread local storage in clang for a successful build.
Alexey will be putting up an updated clang later today with tls enabled.

Also clang on windows is bleeding edge and cmake from git is required thanks to this bug
http://www.gccxml.org/Bug/view.php?id=13035

when cmake 3.0 is out in a few days we will switch and this should work like a charm for everyone