[release-branch.go1.15] cmd/link/internal/ld/pe: fix segfault adding resource section

The resource symbol may have been copied to the mmap'd
output buffer. If so, certain conditions can cause that
mmap'd output buffer to be munmap'd before we get a chance
to use it. To avoid any issues we copy the data to the heap
when the resource symbol exists.

Fixes #42384

Change-Id: I32ef5420802d7313a3d965b8badfbcfb9f0fba4a
GitHub-Last-Rev: 7b0f43011d06083ee3e871e48a87847636f738f9
GitHub-Pull-Request: golang/go#42427
Reviewed-on: https://go-review.googlesource.com/c/go/+/268018


Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Trust: Carlos Amedee <carlos@golang.org>