Adjust is_cr_convertible

If To is const& then From doesn't need to be &.

src/hb-meta.hh

@@ -116,10 +116,16 @@ template <typename T> using hb_remove_pointer = typename hb_match_pointer<T>::ty
 /* TODO Add feature-parity to std::decay. */
 template <typename T> using hb_decay = hb_remove_const<hb_remove_reference<T>>;
 
-#define hb_is_cr_convertible(From, To) ( \
-	hb_is_same (hb_decay<From>, hb_decay<To>) && \
-	hb_is_const (From) <= hb_is_const (To) && \
-	hb_is_reference (From) >= hb_is_reference (To))
+#define hb_is_cr_convertible(From, To) \
+	( \
+	  hb_is_same (hb_decay<From>, hb_decay<To>) && \
+	  ( \
+	    hb_is_const (From) <= hb_is_const (To) && \
+	    hb_is_reference (From) >= hb_is_reference (To) \
+	  ) || ( \
+	    hb_is_const (To) && hb_is_reference (To) \
+	  ) \
+	)