Fixed header dependencies to be fully compatible with the Windows
headers (with help from Dimitrie O. Paun).

diff --git a/include/gdi.h b/include/gdi.h
index 850b4a5..85e41b1 100644
--- a/include/gdi.h
+++ b/include/gdi.h
@@ -21,7 +21,9 @@
 #ifndef __WINE_GDI_H
 #define __WINE_GDI_H
 
+#include <stdarg.h>
 #include <windef.h>
+#include <winbase.h>
 #include <wingdi.h>
 #include <wine/wingdi16.h>
 #include <math.h>