cmd/compile/internal/typecheck: push ONEW into go/defer wrappers

cmd/compile/internal/typecheck: push ONEW into go/defer wrappers

Currently, we rewrite:

	go f(new(T))

into:

	tmp := new(T)
	go func() { f(tmp) }()

However, we can both shrink the closure and improve escape analysis by
instead rewriting it into:

	go func() { f(new(T)) }()

This CL does that.

Change-Id: Iae16a476368da35123052ca9ff41c49159980458
Reviewed-on: https://go-review.googlesource.com/c/go/+/520340
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>