cmd/compile: fix failure to communicate between ABIinfo producer&consumer

ABI info producer and consumer had different ideas for register
order for parameters.

Includes a test, includes improvements to debugging output.

Updates #44816.

Change-Id: I4812976f7a6c08d6fc02aac1ec0544b1f141cca6
Reviewed-on: https://go-review.googlesource.com/c/go/+/299570


Trust: David Chase <drchase@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>