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/enhmetafile.c b/objects/enhmetafile.c
index 6c5f76a..920bfbb 100644
--- a/objects/enhmetafile.c
+++ b/objects/enhmetafile.c
@@ -43,6 +43,7 @@
 #include "winnls.h"
 #include "winerror.h"
 #include "gdi.h"
+#include "gdi_private.h"
 #include "wine/debug.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(enhmetafile);