[dev.regabi] cmd/compile: merge ascompatee, ascompatee1, and reorder3

These functions are interelated and have arbitrarily overlapping
responsibilities. By joining them together, we simplify the code and
remove some redundancy.

Passes toolstash -cmp.

Change-Id: I7c42cb7171b3006bc790199be3fd0991e6e985f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/280438


Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>