cmd/compile: use NoXPos instead of lineno in typenod

typenod is only used for anonymous types, which don't logically have
position information.

Passes toolstash-check.

Updates #19683.

Change-Id: I505424ae980b88c7deed5f23502c3cecb3dc0702
Reviewed-on: https://go-review.googlesource.com/80298
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -237,7 +237,7 @@ func dclname(s *types.Sym) *Node {
 }
 
 func typenod(t *types.Type) *Node {
-	return typenodl(lineno, t)
+	return typenodl(src.NoXPos, t)
 }
 
 func typenodl(pos src.XPos, t *types.Type) *Node {