[HB] Minor cleanup

src/hb-ot-layout-gdef-private.hh

diff --git a/src/hb-ot-layout-gdef-private.hh b/src/hb-ot-layout-gdef-private.hh
index 2a96a64..ba34e3a 100644
--- a/src/hb-ot-layout-gdef-private.hh
+++ b/src/hb-ot-layout-gdef-private.hh
@@ -300,7 +300,7 @@
 
 struct GDEF
 {
-  static const hb_tag_t Tag		= HB_TAG ('G','D','E','F');
+  static const hb_tag_t Tag	= HB_OT_TAG_GDEF;
 
   enum {
     UnclassifiedGlyph	= 0,

src/hb-ot-layout-gpos-private.hh

diff --git a/src/hb-ot-layout-gpos-private.hh b/src/hb-ot-layout-gpos-private.hh
index c245e0f..4aaefeb 100644
--- a/src/hb-ot-layout-gpos-private.hh
+++ b/src/hb-ot-layout-gpos-private.hh
@@ -1487,7 +1487,7 @@
 
 struct GPOS : GSUBGPOS
 {
-  static const hb_tag_t Tag		= HB_TAG ('G','P','O','S');
+  static const hb_tag_t Tag	= HB_OT_TAG_GPOS;
 
   static inline const GPOS& get_for_data (const char *data)
   { return (const GPOS&) GSUBGPOS::get_for_data (data); }

src/hb-ot-layout-gsub-private.hh

diff --git a/src/hb-ot-layout-gsub-private.hh b/src/hb-ot-layout-gsub-private.hh
index 535d636..db608fd 100644
--- a/src/hb-ot-layout-gsub-private.hh
+++ b/src/hb-ot-layout-gsub-private.hh
@@ -823,7 +823,7 @@
 
 struct GSUB : GSUBGPOS
 {
-  static const hb_tag_t Tag		= HB_TAG ('G','S','U','B');
+  static const hb_tag_t Tag	= HB_OT_TAG_GSUB;
 
   static inline const GSUB& get_for_data (const char *data)
   { return (const GSUB&) GSUBGPOS::get_for_data (data); }

src/hb-ot-layout-gsubgpos-private.hh

diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 0682691..2f95674 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -835,8 +835,8 @@
 
 struct GSUBGPOS
 {
-  static const hb_tag_t GSUBTag		= HB_TAG ('G','S','U','B');
-  static const hb_tag_t GPOSTag		= HB_TAG ('G','P','O','S');
+  static const hb_tag_t GSUBTag	= HB_OT_TAG_GSUB;
+  static const hb_tag_t GPOSTag	= HB_OT_TAG_GPOS;
 
   STATIC_DEFINE_GET_FOR_DATA_CHECK_MAJOR_VERSION (GSUBGPOS, 1, 1);