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>