support windows 8

From bruen...@google.com on September 28, 2011 11:32:20

despite the new WinRT, the third-party information I've seen indicates that the Native API is pretty much the same with just a few additions, so at our level WinRT may not mean much change at all. but, we need to actually investigate first-hand, and update the version and syscall checks, etc.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=565