Make it an error to include non-top-level headers
Users should #include <hb.h> (or hb-ft.h, hb-glib.h, etc), but
never things like hb-shape.h directly. This makes it easier to
refactor headers later on without breaking compatibility.
diff --git a/src/hb-private.hh b/src/hb-private.hh
index c757e2d..f561260 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -33,7 +33,10 @@
#include "config.h"
#endif
-#include "hb-common.h"
+#include "hb.h"
+#include "hb-ot.h"
+#define HB_H_IN
+#define HB_OT_H_IN
#include <stdlib.h>
#include <stddef.h>
