Minor

src/hb-ft.cc

diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index 22c7f1b..25368f1 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -325,7 +325,7 @@
   return hb_face_reference ((hb_face_t *) ft_face->generic.data);
 }
 
-void
+static void
 _do_nothing (void)
 {
 }