Add DECL_ATTR_KINDS

Author: kimdv

CodeGeneration/Sources/SyntaxSupport/AttributeKinds.swift.gyb

@@ -86,6 +86,38 @@ public let TYPE_ATTR_KINDS = [
 % end
 ]
 
+// Schema for `DeclAttribute`s:
+//
+// - Attribute name.
+// - C++ class name without the 'Attr' suffix
+// - Options for the attribute, including:
+//    * the declarations the attribute can appear on
+//    * whether duplicates are allowed
+// - Unique attribute identifier used for serialization. This
+//   can never be changed.
+//
+// SimpleDeclAttribute is the same, but the class becomes
+// SimpleDeclAttr<DAK_##NAME> on the C++ side.
+//
+// Please help ease code review/audits:
+// - Please place the "OnXYZ" flags together on the next line.
+// - Please place the non-OnXYZ flags together on the next to last line.
+// - Please place the unique code number on the last line.
+// - Please sort attributes by serialization number.
+// - Please create a "NOTE" comment if a unique number is skipped.
+//
+// If you're adding a new kind of "attribute" that is spelled without a leading
+// '@' symbol, add an entry to the `DECL_MODIFIER_KINDS` array instead.
+//
+// If you're adding a new underscored attribute here, please document it in
+// docs/ReferenceGuides/UnderscoredAttributes.md.
+public let DECL_ATTR_KINDS: [Attribute] = [
+% for attr in DECL_ATTR_KINDS:
+  ${make_swift_attribute(attr)},
+% end
+]
+
+
 /// Schema for declaration modifiers:
 ///
 /// - Modifier name.