[dev.unified] go/internal: set underlying types in proper order

[dev.unified] go/internal: set underlying types in proper order

This problem appeared in google-internal testing.
If the run-later functions are run in the wrong order,
type definitions won't resolve properly.

Change-Id: I9da0775976282e92ca036d20fd9fd6650900daf9
Reviewed-on: https://go-review.googlesource.com/c/go/+/419996
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>