Use ::GetVersionEx directly rather than the Win8.1 SDK helpers

This removes ifdefs and fixes the build for users of the Win8.0 SDK,
which I happen to be. Upgrading is not hard, but executing the same code
everywhere seems better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257379 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed