cmd/compile: preserve argument order in debug_info

When regabi is used sorting by stack offset will not preserve the order
of function arguments. Trust that variables are already ordered
correctly when creating debug_info entries.

Fixes #45720

Change-Id: I1dbdd185975273f70244a23302d34f082347603d
Reviewed-on: https://go-review.googlesource.com/c/go/+/315280


Reviewed-by: Than McIntosh <thanm@google.com>
Trust: Jeremy Faller <jeremy@golang.org>