[config] Add HB_NO_OT_LAYOUT_UNUSED

Part of https://github.com/harfbuzz/harfbuzz/issues/1652

src/hb-config.hh

@@ -44,6 +44,7 @@
 #define HB_NO_BITMAP
 #define HB_NO_CFF
 #define HB_NO_MATH
+#define HB_NO_OT_LAYOUT_UNUSED
 #endif
 
 #ifdef HB_MINI

src/hb-ot-layout.cc

@@ -335,6 +335,12 @@ hb_ot_layout_get_attach_points (hb_face_t      *face,
 				unsigned int   *point_count /* IN/OUT */,
 				unsigned int   *point_array /* OUT */)
 {
+#ifdef HB_NO_OT_LAYOUT_UNUSED
+  if (point_count)
+    *point_count = 0;
+  return 0;
+#endif
+
   return face->table.GDEF->table->get_attach_points (glyph,
 						     start_offset,
 						     point_count,
@@ -364,6 +370,12 @@ hb_ot_layout_get_ligature_carets (hb_font_t      *font,
 				  unsigned int   *caret_count /* IN/OUT */,
 				  hb_position_t  *caret_array /* OUT */)
 {
+#ifdef HB_NO_OT_LAYOUT_UNUSED
+  if (caret_count)
+    *caret_count = 0;
+  return 0;
+#endif
+
   unsigned int result_caret_count = 0;
   unsigned int result = font->face->table.GDEF->table->get_lig_carets (font, direction, glyph, start_offset, &result_caret_count, caret_array);
   if (result)