[c++20] P0780R2: Support pack-expansion of init-captures.

This permits an init-capture to introduce a new pack:

  template<typename ...T> auto x = [...a = T()] { /* a is a pack */ };

To support this, the mechanism for allowing ParmVarDecls to be packs has
been extended to support arbitrary local VarDecls.

llvm-svn: 361300
diff --git a/clang/lib/AST/TextNodeDumper.cpp b/clang/lib/AST/TextNodeDumper.cpp
index f287e96..c15713b 100644
--- a/clang/lib/AST/TextNodeDumper.cpp
+++ b/clang/lib/AST/TextNodeDumper.cpp
@@ -1366,6 +1366,8 @@
       break;
     }
   }
+  if (D->isParameterPack())
+    OS << " pack";
 }
 
 void TextNodeDumper::VisitBindingDecl(const BindingDecl *D) {