[release-branch.go1.16] cmd/link: don't cast end address to int32

When linking a very large binary, the section address may not fit
in int32. Don't truncate it.

Fixes #46128.
Updates #46126.

Change-Id: Ibcc8d74bf5662611949e547ce44ca8b973de383f
Reviewed-on: https://go-review.googlesource.com/c/go/+/319289


Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
(cherry picked from commit af0f8c14)
Reviewed-on: https://go-review.googlesource.com/c/go/+/319369