[dev.typeparams] cmd/compile/internal/types2: fix make with type parameter argument

For make with a type parameter argument, the structural type of
the type parameter's constraint determines what make is making.

Change-Id: I3b48f8ce3236b7624e0638b5f5be208c5915c987
Reviewed-on: https://go-review.googlesource.com/c/go/+/339899


Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>