Prefer C linkage

src/hb-unicode.h

diff --git a/src/hb-unicode.h b/src/hb-unicode.h
index 2f4f69b..8aeba33 100644
--- a/src/hb-unicode.h
+++ b/src/hb-unicode.h
@@ -31,6 +31,7 @@
 
 HB_BEGIN_DECLS
 
+
 /* Unicode General Category property */
 typedef enum
 {