Move _WIN32_WINNT definition from command line to e_os.h. The change is

inspired by VC6 failure report. In addition abstain from taking screen
snapshots when running in NT service context.

crypto/rand/rand_win.c

@@ -632,7 +632,8 @@ int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam)
 void RAND_screen(void) /* function available for backward compatibility */
 {
 	RAND_poll();
-	readscreen();
+	if (GetVersion() >= 0x80000000 || !OPENSSL_isservice())
+		readscreen();
 }