cmd/compile: make translation to calls for SSA look more "value-oriented"

The existing translation assumes an in-memory return values, thus it returns
the address of the result(s).  Most consumers immediately load from the
address to get the value, and in late call expansion that is the favored idiom,
and it is also the favored idiom when arguments and results use registers
instead of memory.

Change-Id: Ie0ccc70f399682a42509d847b330ef3956462d56
Reviewed-on: https://go-review.googlesource.com/c/go/+/240186


Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>