windows.h is only included if _WIN32 is predefined

(required for 16-bit DOS compiler compatibility).

xtrn/sdk/xsdk.h

@@ -46,9 +46,11 @@
 	#include <io.h>
 	#include <dos.h>
 	#include <share.h>
-	#include <windows.h>
 	#include <conio.h>
 #endif
+#ifdef _WIN32
+	#include <windows.h>
+#endif
 #include <time.h>
 #include <ctype.h>
 #include <stdio.h>