Avoid Windows 8 Getversion deprecated errors.

Avoid Windows 8 Getversion deprecated errors.

Windows 8 SDKs complain that GetVersion() is deprecated.

We only use GetVersion like this:

	(GetVersion() < 0x80000000)

which checks if the Windows version is NT based. Use a macro check_winnt()
which uses GetVersion() on older SDK versions and true otherwise.
(cherry picked from commit a4cc3c8041104896d51ae12ef7b678c31808ce52)