[release-branch.go1.19] syscall: fix invalid unsafe.Pointer conversion on Windows

[release-branch.go1.19] syscall: fix invalid unsafe.Pointer conversion on Windows

This cherry-pick CL 471335 without using unsafe.{Add,Slice}.

Fixes #58773

Change-Id: Ifa5c059ed5e358ed98aee7e83b95dd1806b535f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/471335
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/471935
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>