Convert boolean enum class consts to static constexpr

Part of https://github.com/harfbuzz/harfbuzz/issues/1553

src/hb-aat-layout-common.hh

diff --git a/src/hb-aat-layout-common.hh b/src/hb-aat-layout-common.hh
index 431a12b..133e873 100644
--- a/src/hb-aat-layout-common.hh
+++ b/src/hb-aat-layout-common.hh
@@ -669,7 +669,7 @@
 
 struct ObsoleteTypes
 {
-  enum { extended = false };
+  static constexpr bool extended = false;
   typedef HBUINT16 HBUINT;
   typedef HBUINT8 HBUSHORT;
   typedef ClassTable<HBUINT8> ClassTypeNarrow;
@@ -699,7 +699,7 @@
 };
 struct ExtendedTypes
 {
-  enum { extended = true };
+  static constexpr bool extended = true;
   typedef HBUINT32 HBUINT;
   typedef HBUINT16 HBUSHORT;
   typedef Lookup<HBUINT16> ClassTypeNarrow;

src/hb-aat-layout-kerx-table.hh

diff --git a/src/hb-aat-layout-kerx-table.hh b/src/hb-aat-layout-kerx-table.hh
index b86c513..db855f3 100644
--- a/src/hb-aat-layout-kerx-table.hh
+++ b/src/hb-aat-layout-kerx-table.hh
@@ -210,7 +210,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = true };
+    static constexpr bool in_place = true;
     enum
     {
       DontAdvance	= Format1EntryT::DontAdvance,
@@ -471,7 +471,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = true };
+    static constexpr bool in_place = true;
     enum Flags
     {
       Mark		= 0x8000,	/* If set, remember this glyph as the marked glyph. */

src/hb-aat-layout-morx-table.hh

diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index d8a90bb..05b5081 100644
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -54,7 +54,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = true };
+    static constexpr bool in_place = true;
     enum Flags
     {
       MarkFirst		= 0x8000,	/* If set, make the current glyph the first
@@ -204,7 +204,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = true };
+    static constexpr bool in_place = true;
     enum Flags
     {
       SetMark		= 0x8000,	/* If set, make the current glyph the marked glyph. */
@@ -425,7 +425,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = false };
+    static constexpr bool in_place = false;
     enum
     {
       DontAdvance	= LigatureEntryT::DontAdvance,
@@ -661,7 +661,7 @@
 
   struct driver_context_t
   {
-    enum { in_place = false };
+    static constexpr bool in_place = false;
     enum Flags
     {
       SetMark		= 0x8000,	/* If set, mark the current glyph. */

src/hb-dsalgs.hh

diff --git a/src/hb-dsalgs.hh b/src/hb-dsalgs.hh
index 75ff456..9cfa290 100644
--- a/src/hb-dsalgs.hh
+++ b/src/hb-dsalgs.hh
@@ -553,26 +553,26 @@
 
 struct HbOpOr
 {
-  enum { passthru_left = true };
-  enum { passthru_right = true };
+  static constexpr bool passthru_left = true;
+  static constexpr bool passthru_right = true;
   template <typename T> static void process (T &o, const T &a, const T &b) { o = a | b; }
 };
 struct HbOpAnd
 {
-  enum { passthru_left = false };
-  enum { passthru_right = false };
+  static constexpr bool passthru_left = false;
+  static constexpr bool passthru_right = false;
   template <typename T> static void process (T &o, const T &a, const T &b) { o = a & b; }
 };
 struct HbOpMinus
 {
-  enum { passthru_left = true };
-  enum { passthru_right = false };
+  static constexpr bool passthru_left = true;
+  static constexpr bool passthru_right = false;
   template <typename T> static void process (T &o, const T &a, const T &b) { o = a & ~b; }
 };
 struct HbOpXor
 {
-  enum { passthru_left = true };
-  enum { passthru_right = true };
+  static constexpr bool passthru_left = true;
+  static constexpr bool passthru_right = true;
   template <typename T> static void process (T &o, const T &a, const T &b) { o = a ^ b; }
 };
 

src/hb-ot-kern-table.hh

diff --git a/src/hb-ot-kern-table.hh b/src/hb-ot-kern-table.hh
index 5e75d08..19d321e 100644
--- a/src/hb-ot-kern-table.hh
+++ b/src/hb-ot-kern-table.hh
@@ -160,7 +160,7 @@
 
 struct KernOTSubTableHeader
 {
-  enum { apple = false };
+  static constexpr bool apple = false;
   typedef AAT::ObsoleteTypes Types;
 
   unsigned int tuple_count () const { return 0; }
@@ -215,7 +215,7 @@
 
 struct KernAATSubTableHeader
 {
-  enum { apple = true };
+  static constexpr bool apple = true;
   typedef AAT::ObsoleteTypes Types;
 
   unsigned int tuple_count () const { return 0; }

src/hb-ot-layout.cc

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 179db65..3ded3ad 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1300,7 +1300,7 @@
 struct GSUBProxy
 {
   enum { table_index = 0u };
-  enum { inplace = false };
+  static constexpr bool inplace = false;
   typedef OT::SubstLookup Lookup;
 
   GSUBProxy (hb_face_t *face) :
@@ -1314,7 +1314,7 @@
 struct GPOSProxy
 {
   enum { table_index = 1u };
-  enum { inplace = true };
+  static constexpr bool inplace = true;
   typedef OT::PosLookup Lookup;
 
   GPOSProxy (hb_face_t *face) :