P0217R3: Parsing support and framework for AST representation of C++1z
decomposition declarations.

There are a couple of things in the wording that seem strange here:
decomposition declarations are permitted at namespace scope (which we partially
support here) and they are permitted as the declaration in a template (which we
reject).

llvm-svn: 276492
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index e07bf48..8918e18 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -598,6 +598,7 @@
     case CXXConversion:
     case EnumConstant:
     case Var:
+    case Binding:
     case ImplicitParam:
     case ParmVar:
     case ObjCMethod:
@@ -678,6 +679,7 @@
     case Captured:
     case TranslationUnit:
     case ExternCContext:
+    case Decomposition:
 
     case UsingDirective:
     case BuiltinTemplate: