cmd/compile/internal/compare: simplify unit test framework
This CL refactors the compare unit tests to be simpler and to stop
using the types API in non-idiomatic ways, to facilitate further
refactoring of the API.
Change-Id: I864a66b2842a0d8dd45f4e3d773144d71666caf2
Reviewed-on: https://go-review.googlesource.com/c/go/+/521275
Auto-Submit: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>