cmd/compile: move Node.Pack to Node.Name.Pack

$ sizeof -p cmd/compile/internal/gc Node
Node 232
$

Change-Id: I4be025f4ec11f882f24ae7582821d36d3b122b77
Reviewed-on: https://go-review.googlesource.com/10526
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/export.go

@@ -416,6 +416,7 @@ func pkgtype(s *Sym) *Type {
 		t := typ(TFORW)
 		t.Sym = s
 		s.Def = typenod(t)
+		s.Def.Name = new(Name)
 	}
 
 	if s.Def.Type == nil {