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 a4cc3c8041)

crypto/rand/rand_win.c

@@ -750,7 +750,7 @@ static void readscreen(void)
   int		y;		/* y-coordinate of screen lines to grab */
   int		n = 16;		/* number of screen lines to grab at a time */
 
-  if (GetVersion() < 0x80000000 && OPENSSL_isservice()>0)
+  if (check_winnt() && OPENSSL_isservice()>0)
     return;
 
   /* Create a screen DC and a memory DC compatible to screen DC */