Fix more compiler warnings

src/hb-debug.hh

@@ -221,12 +221,14 @@ template <>
 
 template <int max_level, typename ret_t>
 struct hb_auto_trace_t {
+
   explicit inline hb_auto_trace_t (unsigned int *plevel_,
 				   const char *what_,
 				   const void *obj_,
 				   const char *func,
 				   const char *message,
-				   ...) : plevel (plevel_), what (what_), obj (obj_), returned (false)
+				   ...) HB_PRINTF_FUNC(6, 7)
+				   : plevel (plevel_), what (what_), obj (obj_), returned (false)
   {
     if (plevel) ++*plevel;
 
@@ -343,7 +345,7 @@ struct hb_no_trace_t {
 #define TRACE_CLOSURE(this) \
 	hb_auto_trace_t<HB_DEBUG_CLOSURE, hb_void_t> trace \
 	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
-	 "")
+	 " ")
 #else
 #define TRACE_CLOSURE(this) hb_no_trace_t<hb_void_t> trace HB_UNUSED
 #endif
@@ -355,7 +357,7 @@ struct hb_no_trace_t {
 #define TRACE_COLLECT_GLYPHS(this) \
 	hb_auto_trace_t<HB_DEBUG_COLLECT_GLYPHS, hb_void_t> trace \
 	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
-	 "")
+	 " ")
 #else
 #define TRACE_COLLECT_GLYPHS(this) hb_no_trace_t<hb_void_t> trace HB_UNUSED
 #endif
@@ -367,7 +369,7 @@ struct hb_no_trace_t {
 #define TRACE_SANITIZE(this) \
 	hb_auto_trace_t<HB_DEBUG_SANITIZE, bool> trace \
 	(&c->debug_depth, c->get_name (), this, HB_FUNC, \
-	 "");
+	 " ");
 #else
 #define TRACE_SANITIZE(this) hb_no_trace_t<bool> trace
 #endif
@@ -379,7 +381,7 @@ struct hb_no_trace_t {
 #define TRACE_SERIALIZE(this) \
 	hb_auto_trace_t<HB_DEBUG_SERIALIZE, bool> trace \
 	(&c->debug_depth, "SERIALIZE", c, HB_FUNC, \
-	 "");
+	 " ");
 #else
 #define TRACE_SERIALIZE(this) hb_no_trace_t<bool> trace
 #endif