Moved a bunch of definitions from gdi.h into a new gdi_private.h to
make sure we don't use them outside of gdi32.

diff --git a/objects/dib.c b/objects/dib.c
index 43239d8..7b4ba69 100644
--- a/objects/dib.c
+++ b/objects/dib.c
@@ -27,6 +27,7 @@
 #include "bitmap.h"
 #include "gdi.h"
 #include "wownt32.h"
+#include "gdi_private.h"
 #include "wine/debug.h"
 #include "palette.h"