[release-branch.go1.16] cmd/compile: declare inlined result params early for empty returns

The code for delayed declaration of inlined result parameters only
handles non-empty return statements. This is generally okay, because
we already early declare if there are any (non-blank) named result
parameters.

But if a user writes a function with only blank result parameters and
with exactly one return statement, which is empty, then they could end
up hitting the dreaded "Value live at entry" ICE.

This CL fixes the issue by ensuring we always early declare inlined
result parameters if there are any empty return statements.

Fixes #44358.

Change-Id: I315f3853be436452883b1ce31da1bdffdf24d506
Reviewed-on: https://go-review.googlesource.com/c/go/+/293293


TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/296569