cmd/compile: call types2.Unalias to be ready for GODEBUG=gotypesalias=1
types2.Unalias is not needed if we know we have a core or underlying
type. Also, types of declared functions (signatures) cannot be aliases
(this includes tuples).
Fixes #65125.
Change-Id: I1faa26b66f6c646719e830dd661136fae86f3775
Reviewed-on: https://go-review.googlesource.com/c/go/+/556036
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>