Commonise tdesc_feature and makes use of it in gdbserver tdesc

gdb/
	* common/tdesc.c (tdesc_feature::accept): Move to here.
	(tdesc_feature::operator==): Likewise.
	(tdesc_create_reg): Likewise.
	* common/tdesc.h (tdesc_type_kind): Likewise.
	(struct tdesc_type): Likewise.
	(struct tdesc_feature): Likewise.
	* regformats/regdat.sh: Create a feature.
	* target-descriptions.c (tdesc_type_kind): Move from here.
	(tdesc_type): Likewise.
	(tdesc_type_up): Likewise.
	(tdesc_feature): Likewise.
	(tdesc_create_reg): Likewise.

gdbserver/
	* tdesc.c (~target_desc): Remove implictly deleted items.
	(init_target_desc): Iterate all features.
	(tdesc_get_features_xml): Use vector.
	(tdesc_create_feature): Create feature.
	* tdesc.h (tdesc_feature) Remove
	(target_desc): Add features.

gdb/common/tdesc.h

@@ -131,6 +131,99 @@ struct tdesc_reg : tdesc_element
 
 typedef std::unique_ptr<tdesc_reg> tdesc_reg_up;
 
+enum tdesc_type_kind
+{
+  /* Predefined types.  */
+  TDESC_TYPE_BOOL,
+  TDESC_TYPE_INT8,
+  TDESC_TYPE_INT16,
+  TDESC_TYPE_INT32,
+  TDESC_TYPE_INT64,
+  TDESC_TYPE_INT128,
+  TDESC_TYPE_UINT8,
+  TDESC_TYPE_UINT16,
+  TDESC_TYPE_UINT32,
+  TDESC_TYPE_UINT64,
+  TDESC_TYPE_UINT128,
+  TDESC_TYPE_CODE_PTR,
+  TDESC_TYPE_DATA_PTR,
+  TDESC_TYPE_IEEE_SINGLE,
+  TDESC_TYPE_IEEE_DOUBLE,
+  TDESC_TYPE_ARM_FPA_EXT,
+  TDESC_TYPE_I387_EXT,
+
+  /* Types defined by a target feature.  */
+  TDESC_TYPE_VECTOR,
+  TDESC_TYPE_STRUCT,
+  TDESC_TYPE_UNION,
+  TDESC_TYPE_FLAGS,
+  TDESC_TYPE_ENUM
+};
+
+struct tdesc_type : tdesc_element
+{
+  tdesc_type (const std::string &name_, enum tdesc_type_kind kind_)
+    : name (name_), kind (kind_)
+  {}
+
+  virtual ~tdesc_type () = default;
+
+  DISABLE_COPY_AND_ASSIGN (tdesc_type);
+
+  /* The name of this type.  */
+  std::string name;
+
+  /* Identify the kind of this type.  */
+  enum tdesc_type_kind kind;
+
+  bool operator== (const tdesc_type &other) const
+  {
+    return name == other.name && kind == other.kind;
+  }
+
+  bool operator!= (const tdesc_type &other) const
+  {
+    return !(*this == other);
+  }
+};
+
+typedef std::unique_ptr<tdesc_type> tdesc_type_up;
+
+/* A feature from a target description.  Each feature is a collection
+   of other elements, e.g. registers and types.  */
+
+struct tdesc_feature : tdesc_element
+{
+  tdesc_feature (const std::string &name_)
+    : name (name_)
+  {}
+
+  virtual ~tdesc_feature () = default;
+
+  DISABLE_COPY_AND_ASSIGN (tdesc_feature);
+
+  /* The name of this feature.  It may be recognized by the architecture
+     support code.  */
+  std::string name;
+
+  /* The registers associated with this feature.  */
+  std::vector<tdesc_reg_up> registers;
+
+  /* The types associated with this feature.  */
+  std::vector<tdesc_type_up> types;
+
+  void accept (tdesc_element_visitor &v) const override;
+
+  bool operator== (const tdesc_feature &other) const;
+
+  bool operator!= (const tdesc_feature &other) const
+  {
+    return !(*this == other);
+  }
+};
+
+typedef std::unique_ptr<tdesc_feature> tdesc_feature_up;
+
 /* Allocate a new target_desc.  */
 target_desc *allocate_target_description (void);